CHEMISTRY  IN  DAILY  LIFE 


CHEMISTRY  IN  DAILY  LIFE 


POPULAR  LECTURES 


BY 


DR.    LASSAR-COHN 

Professor  in  tht  University  of  Konigsberg  ;  Author  of  "  A  Laboratory  Manual 
of  Organic  Chemistry,"  etc. 


TRANSLATED    BY 

M.    M.    PATTISON    MUIR,   M.A. 

Fellow  of  Gonville  and  Caius  College,  Cambridge 


TOttf)  Ctoentgsfout  SBoorrcutB  in  tfje  Celt 

FIFTH  EDITION,  REVISED  AND  AUGMENTED 


PHILADELPHIA 

J.   B.   LIPPINCOTT   COMPANY 

LONDON  :   H.  GREVEL  &  CO. 

1913 


PRINTED  BY 

HAZBLL,  WATSON  AND  VTNEY,   LD. 

LONDON  AND  AYLESBUHV, 

ENGLAND. 


PREFACE 

TO      THE       FIFTH       EDITION 

PROFESSOR  LASSAR-COHN'S  book  has  been  translated  into 
thirteen  languages ;  Czech,  English,  Finnish,  French,  Hebrew, 
Hungarian,  Italian,  Polish,  Portuguese,  Russian,  Servian, 
Spanish,  and  Swedish.  An  edition  has  been  prepared  for  the 
use  of  German  blind  people.  An  unauthorised  edition  has 
been  published  in  New  York,  with  English  notes,  for  use  as 
a  German  reading  book  in  English  schools. 

Very  considerable  changes  in  the  text,  both  omissions  and 
additions,  have  been  made  by  the  Author  in  preparing  the 
seventh  German  edition.  Most  of  these  changes  and 
additions  have  been  put  into  their  proper  places  in  this  the 
fifth  English  edition. 

M.  M.  P.  M. 

FARNHAM,  April  1913. 


1575 


PRE  FACE 

TO       THE      THIRD       EDITION 

THE  Author  has  been  so  good  as  to  supply  a  few  additions, 
designed  by  him  to  make  the  book  of  more  general  interest, 
and  to  bring  it  up  to  date ;  these  have  been  put  into  their 
proper  places  in  the  text.  He  has  also  allowed  me  to  see 
his  corrected  proofs  for  the  fourth  German  edition. 

I  have  ventured  to  make  a  few  small  changes ;  these 
have  been  submitted  to  Professor  Lassar-Cohn,  and  approved 
by  him. 

M.  M.  P.  M, 

CAMBRIDGE,  November  1904, 


vii 


PRE  FACE 

TO       THE       FIRST       EDITION 

THIS  book,  which  now  appears  in  English,  embodies  the 
substance  of  a  course  of  lectures  delivered  by  Dr.  Lassar- 
Cohn,  Professor  of  Chemistry  in  the  University  of  Konigs- 
berg,  to  a  society  in  that  town  modelled  on  the  celebrated 
Humboldt  Academy  of  Berlin. 

These  lectures,  and  the  publication  of  them  in  book  form, 
caused  quite  a  stir  in  German  circles.  And  it  is  in  the 
hope  that  they  will  prove  at  once  interesting,  instructive, 
and  suggestive  to  English  readers  that  I  have  prepared  a 
translation  at  the  request  of  the  publishers. 

That  the  lectures  cover  a  great  variety  of  topics  will  be 
evident  from  a  glance  at  the  Table  of  Contents.  The 
method  of  treatment  is  eminently  human  and  suggestive. 
The  author  shows  that  chemical  phenomena  are  intimately 
bound  up  with  our  daily  lives,  and  that  whether  we  are 
conscious  of  it  or  not  we  are  constantly  carrying  on  chemical 
operations.  He  also  brings  home  to  us  how  chemical  con- 
siderations play  their  part  in  those  speculations  regarding 
the  physical  universe  that  are  suggested  by  each  fresh  dis- 
covery made  by  science. 

Vague    notions     circulate     in     men's    minds    concerning 


X  PREFACE   TO   THE   FIRST    EDITION 

chemistry.  Some  think  the  chemist  is  a  man  who  con- 
pounds  drugs  and  mixes  pills  ;  and  others  look  on  him  as 
an  astrologer  of  the  modern  sort.  This  book  shows  that 
the  chemist  is  in  a  sense  both  of  these,  and  much  more  than 
both ;  it  causes  the  careful  reader  to  realise  the  permeating 
nature  of  chemical  knowledge,  and  it  teaches  him  that 
chemistry  is  emphatically  the  most  human,  and  for  that 
reason  the  most  fascinating,  of  the  sciences. 

The  book  can  be  followed  intelligently  by  any  reader 
who  gives  it  a  little  care ;  no  special  technical  knowledge 
is  required. 

The  translation  has  been  made  from  a  copy  of  the  original 
book  kindly  lent  by  the  Author  containing  Dr.  Lassar-Cohn's 
corrections  and  additions. 

The  very  few  additions  made  by  the  Translator  are  inclosed 
in  square  brackets. 

M.  M.  P.  M. 
CAMBRIDGE,  May  1896. 


CONTENTS 

LECTURE   I 

PAGE 

Breathing— Physics  and  chemistry— The  weight  of  the  air— Analy- 
sis of  air — Argon — Difference  hetween  inspired  and  expired 
breath — Maintenance  of  the  warmth  of  the  body — Combustion 
— Oxidation — Matches — Yellow  and  red  phosphorus  .  .  i 


LECTURE   II 

Nature  of  flame:  (i)  Candles — Composition  of  fats — Oils — Petro- 
leum— Hydrocarbons — The  elements — Tetravalency  of  the 
atom  of  carbon — Chemical  formulae — The  atom  and  the  mole- 
cule —  Distillation  —  Petroleum  ether  —  Vaseline  —  Paraffin — 
Ozone — Manufacture  of  coal-gas— Nature  of  flame  :  (2)  Cook- 
ing by  gas — Incandescent  gaslights  —  Electric  furnace — 
Acetylene 16 


LECTURE   III 

Food  of  plants — Manuring — Fallow  land — Artificial  manures — 
Bones  —  Superphosphates  —  Potash  salts  —  Manuring  with 
nitrogen — Bases,  acids,  and  salts— Mother-liquor — Food  of 
men  and  animals — Experiments  on  digestion— Albuminoids — 
Fats — Carbohydrates — Milk  and  its  coagulation — Cheese — 
Soxhlet's  extraction  apparatus  —  Fibrin — Serum  —  Artificial 
fodder— Gelatin 36 


xii  CONTENTS 


LECTURE   IV  > 

PAGE 

Mixed  diet— Butter— Margarine— Starch— The  sugars— Ripening 
of  fruits— The  diet  of  diabetic  patients— Fruit-sugar— Bonbons 
— Burnt  sugar  as  a  colouring  material — Cane  sugar — Saccharin 
—The  absorption  of  food — Common  salt — Iron — Importance 
of  cooking— Soups— Bread  making— Boiling  potatoes  «  .  63 


LECTURE   V 

Quantity  of  food  that  must  be  consumed,  and  nutritive  values  of  the 
chief  foods— Fermentation— Wine— Cider  and  perry— Cham- 
pagne—  Mead — Koumiss — Beer — Malt — Spirits — Dry  yeast 
[German  yeast]  —  Brandy — Potato  spirit  —  Vinasse  —  Spirit 
refining — Absolute  alcohol — Methylated  alcohol — Liqueurs  .  89 


LECTURE  VI 

Wine  vinegar — Wood  vinegar— Glacial  acetic  acid — Wood  spirit — 
Acetone— Gunpowder — Greek  fire — Fulminating  mercury — 
Guncotton — Dynamite — Collodion — Blasting  gelatin — Cordite 
— Chlorate  explosives — Wool — Cotton — Silk — Artificial  wool 
[Shoddy] — Carbonising— Mercerised  cotton — Artificial  silk  .  116 


LECTURE  VII 

Tanning— Leather— Removing  hair  from  hides  and  softening  them 
-  Tanning  materials  —  Barks  —  Quebracho  bark  —  Sumac- 
Tanning  extracts— Sole  leather— Alum  tanning— Glove  leather 
—Furriery— Iron  and  chrome  leather— Chamois  leather— Wash 
leather — Parchment— Bleaching  on  meadows — Blueing  washed 
linen— Bleaching  by  chlorine— Bleaching  powder— Antichlors— 
Eau  de  Javet/e— Sulphurous  acid— Persil—  Dyeing— Mordants 
—Lakes — Substantive  colours — Coal  tar  colours — Indigo — 
Alizarin— Colouring  pastes— Colouring  extracts  from  woods— 
Log-wood— Calico  printing 


CONTENTS  Xlil 


LECTURE   VIII 

MM 

Oil-painting — Drying  and  non-drying  oils — Linseed  oil — Varnishes 
—Inks— Cellulose  — Paper- Sizing  paper— Straw  boiling- 
Esparto  grass  boiling — Soda  cellulose — Sulphite  cellulose — 
Silvalin  .  .  .  159 


LECTURE    IX 

Burnt  lime— Potash— Soda  by  Leblanc's  process— Sulphuric  acid- 
Sulphate  of  soda— Nitric  acid — Bleaching  powder — Soda 
crystals — Ammonia  soda  process — Ashes  of  molasses — Ashes 
from  the  washings,  of  wool — Soap — Caustic  alkali — Caustic 
soda — Soft  soaps — Loaded  soaps — Curd  soaps — Hard  and  soft 
waters — Plasters  .  .  .176 


LECTURE   X 

Glass — Glass  mirrors — Potash  and  soda  glass — Quartz  glass — S trass 
— Artificial  precious  stones — Ruby  glass — Milk  glass — Clay — 
Bricks  —  Mortars  —  Lime  sandstone  bricks  —  Cements  — 
Glazing — Pottery —  Stoneware  —  Majolica  ware  —  Porcelain — 
Photography — Lunar  caustic — Chloride,  bromide,  and  iodide 
of  silver — Daguerreotypes — Development  of  the  negative — 
Talbotypes— Albumen  methods — Wet  collodion  processes — 
Dry  silver  bromide  emulsion  plates — Platinotypes — Photo- 
graphy of  the  spectrum — Red  light — Orthochromatic  plates — 
Colour  photography — Chrome-gelatin —Pigment  printing — 
Rontgen  rays — Radio-activity — Radium 199 


LECTURE   XI 

Noble  and  base  metals  —  Ores  —  Gold  —  Platinum — Potassium 
cyanide  —  Silver  —  Relations  of  value  between  gold  and 
silver — Bimetallism — Gold  currency — Reduction  of  metallic 
oxides  —  Roasting  sulphur  compounds  —  Pig  iron  —  Steel — 
Wrought  iron  —  Blast  furnaces  —Slags— Coke  —  Puddling— 


xiv  CONTENTS 

PAGE 

Rolled  iron  — Railways —  Cementation  steel  — Cast  steel- 
Bessemer  steel — Spiegeleisen — Manganese — Dephosphorising 
iron — Soft  steel — Nickel  steel — Chromium  steel — Gas  furnaces 
— Regenerative  furnaces — Open  flame  furnaces — Zinc — Elec- 
tro-deposition of  metals — Potassium — Sodium — Aluminium  .  241 


LECTURE   XII 

ALLOYS  :  Coinage  —  Bronze  —  Patina  —  Brass  —  Tombac  —  Talmi  * 
gold— Nickel    silver— Britannia    metal— Type    metal— Nickel 
steel — Rare  metals 

ALKALOIDS:  Methane— Acetylene  gas— Benzene— Pyridine—Coni- 
ine— Quinoline— Kairine— Antipyrin— Phenacetin  — Narcotine 
—Chloral  —  Ether  —  Hoffman's  drops  —  Chloroform  —  Anti- 
septics— lodoform — Carbolic  acid — Corrosive  sublimate— Sa- 
licylic acid 287 

INDEX  on 


CHEMISTRY  IN  DAILY  LIFE 

LECTURE  I 

Breathing— Physics  and  chemistry— The  weight  of  the  air— Analysis 
of  air — Argon — Difference  between  inspired  and  expired  breath- 
Maintenance  of  the  warmth  of  the  body — Combustion — Oxidation  - 
Matches — Yellow  and  red  phosphorus. 

IN  the  lectures  which  begin  to-day  I  hope  to  convince  you 
that  a  foundation  of  chemical  knowledge  is  needed  for  under- 
standing many  occurrences  of  everyday  life.  We  shall  see 
that  there  are  many  facts  which  have  become  so  familiar 
to  us  by  custom  that  we  pay  scarcely  any  heed  to  them,  and 
seldom  give  ourselves  the  trouble  of  thinking  about  the 
more  intimate  relations  of  them. 

Let  us  begin  by  considering  an  action  which  we  perform 
constantly — the  action,  namely,  of  breathing.  We  speak  of 
the  duration  of  our  lives  as  the  time  between  our  first  and 
last  breaths. 

At  once  we  are  faced  by  the  question,  What  do  we  breathe, 
and  for  what  purpose  do  we  breathe  ?  Every  one  knows 
that  we  breathe  the  air  which  surrounds  us.  But  what  is 
this  air? 

Here  it  is  necessary  to  make  a  short  excursion  into  the 
domain  of  physics,  which  is  a  branch  of  science  that  concerns 
itself  with  occurrences,  such  as  the  magnetisation  of  iron, 

i 


2  CHEMISTRY  IN   DAILY  LIFE 

wherein  no  change  of  material  composition  takes  place. 
Chemistry,  on  the  other  hand,  is  that  part  of  natural 
knowledge  whose  task  it  is  to  investigate  events,  such,  for 
instance,  as  the  rusting  of  iron,  wherein  changes  of  material 
composition  do  take  place.  When  a  piece  of  iron  is 
magnetised,  it  is  not  changed  internally  or  externally  from 
its  former  condition,  except  that  it  acquires  the  power  of 
attracting  other  small  pieces  of  iron  ;  on  the  other  hand,  when 
iron  rusts,  it  is  changed  into  a  brown  substance  which  is 
something  quite  different  from  iron — for  instance,  it  is  not 
rigid  like  iron,  but  can  be  rubbed  to  powder  between  the 
fingers. 

To  return  to  our  main  theme.  Is  the  air  something  which 
has  an  actual  material  existence,  or  is  it  only  existent  in  our 
imagination?  For  it  cannot  be  asserted  that  any  one  pos- 
sesses a  sense-organ  whereby  he  can  discover  the  actual 
existence  of  air.  We  talk,  indeed,  of  the  heaviness  of  the 
air ;  but  I  fancy  there  is  scarcely  one  among  those  present 
who  is  able  to  determine  accurately  the  weight  of  a  definite 
quantity  of  air — say,  for  instance,  the  weight  in  kilograms  of 
the  air  in  the  room  wherein  we  are  assembled. 

We  cannot  directly  convince  ourselves  that  the  air  is 
heavy.  We  wave  our  hands  to  and  fro  in  the  air  without 
any  apparent  hindrance  ;  we  even  move  our  whole  bodies 
without  trouble  through  the  air.  And  although  these  facts, 
and  many  other  similar  facts,  seem  entirely  to  contradict 
the  notion  that  air  is  heavy,  nevertheless  every  one  knows 
to-day  that  air  weighs  something.  But  this  is  only  because 
every  one  has  been  accustomed  from  his  youth  to  hear  this 
property  of  air  spoken  of  with  absolute  certainty. 

If  we  consider  a  little,  we  shall  find  many  other  well- 
established  facts  in  the  domain  of  natural  science  which  no 


THE   WEIGHT  OF  AIR  3 

one  doubts,  although  these  facts  cannot  be  demonstrated 
directly.  For  instance,  every  one  admits  that  the  shape  of 
the  earth  is  that  of  a  sphere,  although  no  proof  of  this  has 
yet  been  found  that  can  be  grasped  without  much  difficulty 
by  lay  minds.* 

We  are,  however,  in  a  better  position  in  dealing  with  the 
case  before  us,  inasmuch  as  we  can  easily  convince  ourselves 
of  the  weight,  and  hence  of  the  material  existence,  of  the 
atmosphere.  For  this  purpose  let  us  carry  out  a  simple 
experiment. 

The  flask  A  (fig.  i)  is  placed  on  one  pan  of  a  balance,  and 
the  beam  is  brought  into  equilibrium  by  placing  weights  on 
the  other  pan.  The  special  things  to  be  noticed  about  this 
flask  are,  that  the  neck  has  been  drawn  out  to  a  fine  opening, 
that  the  air  has  then  been  pumped  out  of  the  flask  by  means 
of  an  air-pump,  and  that  the  neck  has  then  been  sealed  by 
melting  the  glass ;  the  interior  of  the  flask  is  evidently  cut  off 
from  the  air  outside.  When  I  now  break  the  end  of  the  neck 
of  the  flask  by  means  of  pliers,  the  pan  in  which  the  flask 
rests  sinks,  although  the  flask  cannot  have  been  made  heavier 
by  cutting  off  the  end  of  the  neck.  The  cause  of  this 
occurrence  is  that  air  rushes  into  the  flask  through  the 
opened  neck,  and  the  heaviness  of  this  air  is  made  visible  to 
us  by  the  descent  of  the  balance-pan.  If  we  know  the 
capacity  of  the  flask,  and  if  we  now  place  weights  on  the 

*  The  fact  that  at  sea  the  tops  of  the  masts  of  an  approaching  vessel 
are  the  first  parts  of  her  to  be  seen  is  often  adduced  as  the  simplest  proof 
of  the  curvature  of  the  earth's  surface  caused  by  the  spherical  form  of  the 
earth.  Although  the  Greeks  and  Romans  often  observed  the  phenomenon 
in  question,  yet  they  did  not  draw  the  conclusion  that  the  earth  is  spherical ; 
but  among  them  were  many  clear-headed  men.  The  alleged  proof 
is  quite  inconclusive  of  itself,  and  it  came  to  the  front  only  after  the 
spherical  form  of  the  earth  had  been  established  on  the  basis  of  strictly 
scientific  investigations. 


4  CHEMISTRY   IN    DAILY   LIFE 

other  pan  till  equilibrium  is  re-established,  we  can  read 
off  directly  the  weight  of  the  air  which  has  rushed  into  and 
filled  the  flask.  Careful  experiments  have  shown  that  one 
litre  of  air  weighs  1-295  grams  [one  cubic  foot  weighs  564 
grains]. 

If  air  is  a  material  thing,  it  must  exert  a  pressure,  because 
of  its  weight,  on  every  object  whereon  it  impinges.  Fore- 
stalling what  is  to  be  dealt  with  later,  we  shall  at  once 


Fig.  i. 

convince  ourselves  of  the  justness  of  this  conclusion.  The 
following  simple  experiment  will  serve  our  purpose.  We 
take  a  flask  which  has  been  sealed  after  all  the  air  has  been 
pumped  out  of  it,  and  bring  the  neck  under  water  as  shown  in 
the  figure  (fig.  2)  ;  we  then  break  off  the  end  of  the  neck.  We 
see  the  water  at  once  rush  rapidly  into  the  flask  and  fill  it. 
The  reason  of  this  is  that  the  air  outside  the  flask  presses  on 
the  surface  of  the  water  in  the  vessel,  and,  inasmuch  as  there 
is  no  contrary  pressure  inside  the  flask  from  which  the  air 


COMPOSITION   OF  THE  AIR  5 

has  been  exhausted,  this  pressure  causes  the  water  to  rush 
inwards  through  the  opened  neck  of  the  flask. 

Had  we  conducted  a  similar  experiment,  using  a  very  long 
tube  in  place  of  the  flask,  we  should  have  noticed  that 
the  pressure  of  the  air  would  have  held  up  the  water  to  a 
height  of  more  than  10  metres.  If  in  place  of  water  we  use 
mercury,  a  liquid  which  is  about  13-5  times  heavier  than 
water,  the  air  will  press  this  upwards  to  a  height  about  13*5 
times  less  than  that  to  which  it  forces  water — that  is,  in 
round  numbers,  to  a  height 
of  760  millimetres  [30  inches]. 
A  column  of  mercury  30 
inches  high  is  in  equilibrium 
with  the  pressure  of  the  at- 
mosphere, and  as  the  latter 
increases  or  decreases  the 
mercury  in  the  tube  rises  or 
falls.  For  this  reason  we 
make  use  of  such  a  column  of  ~  - 

mercury,  under  the  name  of  Fig.  2. 

barometer  (derived   from   the 

Greek  word  ffapus  —  heavy),  as  a  measure  of  the  weight,  or 
more  correctly  of  the  pressure,  of  the  atmosphere. 

By  this  time  we  know  that  the  air  is  a  material  substance. 
But  now  comes  the  question  :  is  air  a  homogeneous  body,  or 
is  it  made  up  of  several  constituents? 

It  can,  evidently,  be  no  easy  task  to  analyse — that  is,  to 
test  for  its  constituents — something  which  we  are  unable  to 
grasp  in  our  hands  or  to  see  with  our  eyes  ;  and,  indeed,  the 
solution  of  this  most  ancient  problem  was  partially  gained 
only  about  a  hundred  years  ago. 

It  is  possible  to  demonstrate  to  you,  without  assuming  any 


6  CHEMISTRY    IN    DAILY   LIFE 

chemical  knowledge  on  your  part,  that  air  must  contain  at 
least  two  components — one,  namely,  which  maintains  com- 
bustion, and  another  which  does  not  do  this. 

For  this  purpose  we  proceed  as  follows.  By  immersing  a 
glass  jar  in  water  we  cut  off  a  definite  volume  of  air  from 
the  rest  of  the  atmosphere.  A  little  piece  of  phosphorus  is 
placed  in  a  small  basin  which  is  floated  on  the  surface  of  the 
water  inside  the  jar  (see  fig.  3).  I  now  remove  the  jar, 


*'ig.  3-  Fig.  4. 

ignite  the  phosphorus,  and  again  place  the  jar  over  the  little 
basin.  The  phosphorus  continues  to  burn  brightly  for  a 
short  time,  while  it  combines  with  a  part  of  the  air  in  the 
jar,  and  then  goes  out.  While  this  is  going  on,  the  external 
air-pressure  forces  water  into  the  jar,  to  take  the  place  of 
the  air  which  has  been  removed,  and  the  removal  of  which 
has  produced  a  partial  vacuum  in  the  jar,  and  the  quantity 
of  water  so  driven  into  the  jar  corresponds  with  the  quantity 
of  air  which  has  combined  with  the  phosphorus  (fig.  4). 


COMPOSITION   OF  THE  AIR  7 

An  examination  of  the  gas  left  in  the  jar  shows  that  it 
differs  from  the  atmosphere  around  us  in  that  a  burning 
body,  even  a  substance  so  combustible  as  phosphorus,  goes 
out  when  brought  into  this  gas  ;  and  in  many  other  respects 
the  gas  is  found  to  be  very  indifferent — that  is,  it  shows 
scarcely  any  inclination  to  combine  with  other  substances, 
and  so  to  form  new  bodies.  This  gas  is  called  nitrogen. 
Living  things  die  in  it. 

The  other  part  of  the  air  which  combined  with  phosphorus 
in  the  experiment  just  described  is  called  oxygen^  from  the 
Greek  word  ofu?  =  sharp  or  acid.  In  contradistinction  to 
nitrogen,  it  is  an  extremely  active  body — that  is,  it  is  very 
ready  to  form  new  compounds.  We  have  seen  a  case  of 
combustion  (the  combustion  of  phosphorus)  attended  with 
flame,  which  was  brought  about  by  oxygen,  as  indeed  are  all 
the  combustions  that  occur  in  practical  life. 

Oxygen  also  combines  slowly  with  very  many  substances 
without  producing  flame.  The  rusting  of  iron,  for  instance, 
that  is  so  dreaded  by  the  housewife,  depends  on  the  combina- 
tion of  the  metal  with  the  oxygen  of  the  air  to  form  iron 
oxide,  or  rust  as  this  substance  is  commonly  called. 

We  shall  become  acquainted  with  a  whole  series  of  com- 
binations, like  the  rusting  of  iron,  of  bodies  of  very  different 
kinds  with  oxygen ;  such  occurrences  can  scarcely  be  called 
combustions,  because  we  associate  the  appearance  of  fire 
with  combustion.  These  processes  are  called  oxidations. 
The  terminal  syllable  in  the  often  used  term  oxide  means,  as 
we  now  'readily  understand,  nothing  but  a  compound  with 
oxygen.  Lead  oxide  signifies  a  compound  of  lead  and  oxygen, 
and  lead  superoxide  a  similar  compound  containing  twice  as 
much  oxygen,  and  so  on. 

When  an  investigation  is  made  of  the  air  that  surrounds 
us,  with  an  observance  of  all  the  rules  laid  down  by  science, 


8  CHEMISTRY  IN   DAILY  LIFE 

it  is  found  that  air  always  contains  a  very  little  carbonic  acid 
gas  and  some  moisture,  besides  nitrogen  and  oxygen  ;  and 
if  a  determination  is  made  of  the  quantity  of  each  of  these 
in  100  parts  of  air,  the  following  proportions  are  obtained  : 

Nitrogen          78*35  parts. 

Oxygen 2077     „ 

Water  in  the  gaseous  state  ...      0*85  part  (so-called  moisture). 

Carbonic  acid  gas      Q'Q3    » 

ico'oo  parts. 

Chemists  call  these  quantities  calculated  on  100  parts 
percentages  ;  they  say  that  air  contains  78*35  per  cent,  of 
nitrogen,  etc. 

It  has  been  found  recently  that  nitrogen  separated  from 
air  by  a  chemical  method — we  learnt  to  recognise  a  chemical 
process  a  little  while  ago — is  not  a  homogeneous  body,  as 
had  been  supposed,  but  that  it  contains,  mixed  with  it,  very 
small  quantities  of  several  other  gaseous  elements,  which 
have  been  called  argon,  helium,  krypton,  neon,  and  xenon. 
These  elements  are  present  in  the  air  in  such  very  small 
quantities  that  it  is  not  necessary  for  us  to  say  more  about 
them. 


We  are  all  aware  that  the  ability  of  the  air  to  take  up 
moisture,  and  to  deposit  it  again  in  the  form  of  rain,  is  of 
great  importance  in  the  economy  of  nature.  In  daily  life 
also  we  make  constant  use  of  this  capability  of  the  atmo- 
sphere to  take  up  water  ;  for  on  this  depends  the  drying  of 
the  wash,  or  of  a  floor  that  has  been  scrubbed,  etc. 

We  must  not  forget  the  modification  of  oxygen  which 
is  called  ozone,  as  this  substance  is  often  mentioned  in 
ordinary  life, 


INSPIRED  AND   EXPIRED    BREATH  9 

When  we  have  become  acquainted  with  the  conception 
of  the  atom  (see  p.  24),  we  shall  be  in  a  position  to  under- 
stand the  relations  between  ozone  and  ordinary  oxygen 
(see  p.  27). 

In  1896,  Linde  succeeded  in  liquefying  air  by  the  use 
of  an  extraordinarily  ingenious  mechanical  arrangement. 
The  liquid  consists  for  the  most  part  of  oxygen  and  nitrogen, 
which  can  be  separated  by  distillation  (see  p.  25). 

Now  that  we  have  got  to  know  the  composition  of  air, 
the  question  presents  itself  why  we  must  have  air  to  live  in, 
for  experience  tells  us  that  want  of  air  leads  to  suffocation 
and  cessation  of  life. 

This  is  explained  as  follows.  The  air  which  we  in- 
voluntarily breathe  in  finds  its  way  into  the  lungs,  and  there 
comes  into  contact  with  the  blood  by  passing  through  the 
walls  of  the  fine  capillary  veins  wherein  the  blood  is  circu- 
lating. Such  thin  membranes  as  the  coatings  of  the  veins 
are  quite  impermeable  by  liquids,  but  allow  gases  to  pass 
through  them  freely,  or,  to  use  the  technical  expression,  to 
diffuse  through  them.  When,  then,  the  blood  comes  into 
contact  with  the  oxygen  of  the  air  by  diffusion,  the  blood 
absorbs  oxygen,  and  at  the  same  time  gives  up  carbonic  acid 
gas.  We  should  therefore  find  the  expired  breath  to  be  rich 
in  carbonic  acid ;  and  it  is  easy  to  prove  experimentally  that 
this  is  the  case. 

For  this  purpose  we  will  draw  some  external  air  through 
clear,  filtered  lime-water  by  sucking  with  the  mouth  at  A 
(fig-  5)-  There  is  so  small  a  proportion  of  carbonic  acid 
in  the  air  that  no  visible  change  is  made  in  the  lime-water  in 
the  short  time  during  which  the  experiment  lasts  ;  but  when 
I  blow  expired  breath  through  the  same  lime-water  by  means 
of  the  small  tube  B  (fig.  6),  a  turbidity,  which  is  visible  at 


10  CHEMISTRY   IN    DAILY   LIFE 

some  distance,  quickly  appears  in  the  liquid.  This  means 
that  the  carbonic  acid  gas  in  the  expired  breath  has 
combined  with  the  lime  to  form  chalk,  which,  being  in- 
soluble in  water,  is  diffused  through  the  liquid  as  a  fine 
powder. 

The  following  analysis  of  a  sample  of  expired  breath,  which 
had  been  deprived  of  moisture,  shows  how  considerable  is 
the  quantity  of  carbonic  acid  in  the  breath  sent  out  from 
the  lungs : 

Nitrogen     79-58  per  cent. 

Oxygen        16-04       „ 

Carbonic  acid  gas 4-38        „ 


Fig-  5-  Fig.  6. 


While  the  oxygen  has  been  reduced  by  about  one-fifth,  the 
quantity  of  carbonic  acid  has  been  increased  about  a  hundred- 
and-forty-fold. 

The  oxygen  which  has  been  absorbed  by  the  blood  is 
carried  by  the  blood  through  the  whole  of  the  body,  and 
brings  about  oxidations.  Particularly,  it  burns  to  carbonic 
acid  the  carbon  of  many  substances — which  are  naturally 
always  being  re-formed  by  the  help  of  the  nourishment  taken 
into  the  body— and  the  blood  returning  to  the  lungs  carries 
with  it  this  carbonic  acid  gas,  which  originates  from  the 


MAINTENANCE   OF   THE   WARMTH   OF   THE   BODY         II 

tissues,  etc.,  in  the  most  different  parts  of  the  body,  and  there 
gives  it  up  in  exchange  for  oxygen. 

The  continuous  oxidation  which  takes  place  in  the  body 
as  a  consequence  of  breathing  is  accompanied,  like  every 
other  process  of  burning — for  oxidation  is  merely  another 
name  for  burning — with  the  production  of  heat ;  and  it  is 
this  heat  which  maintains  our  bodies  at  their  normal  tem- 
perature of  37°  C.  [98-4°  F.]. 

When  we  consider  that  the  circulation  of  blood  from  and 
back  to  the  heart  occupies  only  about  ten  seconds  in  a  man, 
we  easily  understand  how  our  bodily  temperature  is  kept 
constant  in  all  parts  of  the  body  by  this  process,  notwith- 
standing that  we  are  continually  parting  with  a  considerable 
quantity  of  heat  to  our  colder  surroundings.  In  a  subsequent 
lecture  we  shall  discover  what  weight  of  carbon  must  be 
burnt  daily  for  this  purpose.  But  even  now  it  is  clear  from 
what  has  been  said  that  the  supply  of  carbon  compounds  in 
the  body  must  soon  be  exhausted  unless  there  be  sufficient 
compensation  ;  and  hence,  as  well  as  to  make  up  for  other 
withdrawals,  we  are  compelled  to  absorb  sufficient  quantities 
of  nourishment. 

Before  leaving  our  present  subject,  we  shall  glance  for 
a  moment  at  the  process  of  combustion,  and  in  the  next 
lecture  we  shall  deal  in  more  detail  with  the  phenomena  of 
flame  which  accompany  combustions,  as  both  of  these  are 
conditioned  by  oxygen,  about  which  we  have  learnt  some- 
thing. 

All  the  materials  used  in  ordinary  life  for  burning  are  rich 
in  carbon  ;  wood  and  turf,  for  instance,  have  been  used  for 
ages,  and  in  more  recent  times  coal  and  peat  have  come 
into  use,  as  fuel.  The  process  of  burning  such  fuels  consists, 
in  the  main,  in  the  combination  of  the  carbon  of  the  fuel  with 


12 


CHEMISTRY   IN    DAILY   LIFE 


the  oxygen  of  the  air  to  form  carbonic  acid,  while  at  the  same 
time  the  small  quantities  of  hydrogen  in  the  materials  are 
burnt  to  water. 

Carbon  and  oxygen  do  not  combine  when  cold  ;  but  if  the 
combination  is  started,  the  material  continues  to  burn,  since 
the  heat  produced  by  the  part  which  is  burning  suffices  to 
make  the  neighbouring  parts  hot  enough  to  begin  burning 
—that  is,  so  hot  that  combination  of  carbon  with  oxygen 


occurs. 


We  cannot  at  present  go  into  the  methods  that  have  been 
so  fully  developed  nowadays  for  the  most  economic  employ- 
ment of  fuel  ;  but  when  we  come  to  speak  of  the  metallurgy 
of  iron,  we  shall  have  occasion  to  learn  something  more  fully 
of  these  methods  in  connection  with  the  processes  for  manu- 
facturing that  metal. 

The  question  as  to  how  combustible  material  is  set  on  fire, 
how  the  burning  is  generally  started,  has  still  to  be  answered. 
Nowadays  it  is  very  easy  :  we  use  matches  ;  but  matches 
came  into  use  only  about  eighty  years  ago.  The  question 
must  always  remain  unanswered  as  to  whether  primitive  man 
became  acquainted  with  fire  by  rubbing  pieces  of  dry  wood 
together,  or  by  obtaining  it  from  a  tree  which  had  been 
ignited  by  a  lightning-flash.  It  is  certain  that  fire  can  be 
obtained  by  rubbing  together  pieces  of  wood  ;  and  travellers 
have  found  this  method  in  use  among  distant  tribes  at  the 
present  time.  The  method,  however,  requires  the  wood  to  be 
drier  than  we  ever  find  it  in  its  natural  state  in  our  climate. 
The  difficulty  of  getting  fire  anew,  and  therefore  the  immense 
importance  of  maintaining  the  fire  which  had  been  started, 
explain  the  fact  that  all  the  older  races  looked  on  the  hearth, 
where  this  supreme  possession  was  maintained  continuously, 
as  a  sacred  place. 


MATCHES  13 

The  process  of  obtaining  fire  by  allowing  the  sparks  pro- 
duced by  striking  a  piece  of  steel  and  a  flint  together  to  fall 
on  to  tinder  or  dry  fungus  was  generally  used  in  the  later 
Middle  Ages. 

Since  the  beginning  of  last  century  isolated  attempts  were 
made  to  devise  a  method  for  getting  fire,  which  could  always 
be  conveniently  applied,  by  employing  some  one  of  the 
processes — and  there  are  many  of  them — in  use  in  chemical 
laboratories.  The  results  of  these  attempts  were  but  small, 
the  methods  themselves  were  very  inconvenient  and  un- 
trustworthy, and  the  apparatus  was  sometimes  absolutely 
dangerous,  until  in  the  thirties  use  was  made  of  phos- 
phorus. 

About  that  time  an  Hungarian  chemist,  Johann  Jrinyi, 
hit  on  the  notion  of  using  phosphorus,  experiments  with 
which  substance  he  had  seen  made  in  a  lecture.  Sulphur- 
matches,  which  were  little  slips  of  wood  tipped  with  sulphur, 
were  in  common  use  at  that  time  for  obtaining  fire ;  Jrinyi 
added  a  little  phosphorus  to  the  sulphur,  and  the  lucifer- 
match  was  made. 

Phosphorus,  as  is  generally  known,  takes  fire  when  rubbed  ; 
the  burning  is  passed  on  by  the  phosphorus  to  the  sulphur, 
and  from  the  sulphur  to  the  wood.  It  was  of  course  not  so 
easy  to  surmount  the  technical  difficulties  and  to  manufacture 
really  good  lucifer  matches.  But  after  a  time  matches  of 
unexceptionable  quality  were  prepared. 

As  a  fire-producing  material  the  lucifer-match  left  nothing 
to  be  desired  ;  but  these  matches  had  other  properties  which 
have  led  to  their  replacement  of  late  years  by  what  are 
generally  called  safety-matches. 

Phosphorus  is  extremely  poisonous ;  the  lucifer-match 
placed  the  general  public  in  possession  of  this  dangerous 


CHEMISTRY  IN   DAILY   LIFE 


substance  ;  and  the  substance  had  also  deadly  effects  on  the 
workers  in  match  factories,  many  of  whom  suffered  from 
terrible  diseases  in  their  bones. 

Ordinary  phosphorus  is  yellow;  but  it  possesses  the 
remarkable  property  of  changing  into  a  red  powder,  known 
as  red  phosphorus,  when  it  is  heated  for  some  time  to  about 
250°  C.  [482°  F.]  in  a  closed  space— heated  in  the  air  of 

course  it  burns — such  as  a 
vessel  with  a  tightly  fitting 
cover.  This  transformation 
can  be  shown  here  easily  in 
the  following  way.  A  small 
quantity  of  yellow  phos- 
phorus is  placed  in  the  glass 
tube  A  (fig.  7),  and  the  tube 
is  closed  by  fusing  together 
the  glass  at  the  open  end  ; 
the  tube  is  then  suspended 
in  a  wider  tube,  wherein 
is  placed  a  liquid  that  boils 
at  250°  C.  [482°  F.].  The 
liquid  is  now  caused  to  boil, 
and  the  tube  A  is  thus  sur- 
rounded by  the  vapour  of 
the  boiling  liquid,  which 

soon    heats  A   to   250°,   and   we  see   the  yellow  phosphorus 
gradually  changing  to  a  red  mass. 

Now  red  phosphorus  is  not  poisonous,  and  it  is  also  much 
more  difficult  to  ignite  than  yellow  phosphorus  ;  it  is,  indeed, 
so  uninflammable  that  it  does  not  take  fire  when  rubbed  on 
any  casual  surface.  To  ignite  red  phosphorus  by  friction 
requires  rubbing  on  a  surface  containing  substances  rich  in 
oxygen.  The  mixture  used  for  making  the  heads  of  safety- 


RED    PHOSPHORUS  I  5 

matches  which  are  ignited  by  rubbing  on  a  surface  prepared 
with  red  phosphorus  consists  of  32  parts  chlorate  of  potash, 
12  parts  chromate  of  potash,  32  parts  peroxide  of  lead,  and 
34  parts  sulphide  of  lead  ;  the  first  three  of  these  substances 
are  characterised  by  the  large  quantities  of  oxygen  they 
contain. 


LECTURE    II 

Nature  of  flame  :  (i)  Candles— Composition  of  fats— Oils— Petroleum- 
Hydrocarbons— The  elements— Tetravalency  of  the  atom  of  carbon 
—Chemical  formulae— The  atom  and  the  molecule— Distillation- 
Petroleum  ether— Vaseline— Paraffin— Ozone— Manufacture  of  coal- 
gas— Nature  of  flame  :  (2)  Cooking  by  gas— Incandescent  gaslights 
—  Electric  furnace— Acetylene. 

IT  is  well  known  that  the  burning  of  substances  which  con- 
tain carbon  serves  not  only  for  the  production  of  heat,  but 
also  for  lighting  purposes.  But  flame  is  produced  only  by 
those  carbon-containing  materials  which  are  converted  into 
gas  or  vapour  when  they  are  burnt  ;  this  will  be  proved  by 
experiment  very  shortly. 

Compounds  which  contain  very  much  carbon,  such  as  wood, 
coal,  or  tallow,  are  not,  indeed,  themselves  volatile,  but  they 
burn  with  a  flame  because  they  give  off  combustible  gases 
when  they  are  heated.  The  flame  is  therefore  nothing  else 
than  a  burning  gas  which  is  constantly  being  produced  from 
the  material. 

If  we  now  set  fire  to  a  piece  of  wood,  we  see  that  it  burns 
with  a  flame  ;  but  if  we  have  previously  removed  from  the 
wood  everything  that  will  volatilise,  by  heating  the  wood 
very  strongly  out  of  contact  with  the  air,  we  find  that  the 
wood  charcoal  thus  produced  will  not  burn  with  a  flame. 

It  is  possible  to  draw  the  gas  out  of  a  flame — out  of  a 

16 


NATURE  OF  FLAME  i; 

candle-flame,  for  instance — and  then  to  burn  the  gas.  The 
method  of  doing  this  is  as  follows.  We  introduce  a  glass 
tube  into  the  flame  ;  one  end  of  this  tube  is  drawn  to  a  point, 
and  the  other  passes  through  a  cork  which  is  fitted  into  a 
cylinder  quite  filled  with  water.  Another  glass  tube  passes 
through  the  cork,  and  reaches  to  the  bottom  of  the  cylinder  ; 
this  tube  is  connected  with  a  piece  of  caoutchouc  tubing,  and 
the  glass  and  caoutchouc  tubes  are  filled  with  water,  and  so 


_>i^«£-_i..=aft.-»_      *-rj*i*m—:^^^-,.  -       :  v. '    •        .  :FiS*w  •• 


Fig.  8. 

act  as  a  syphon  (see  fig.  8).  Water  is  now  allowed  to  flow 
slowly  from  the  caoutchouc  tube  by  partially  opening  a  pinch- 
cock  placed  on  this  tube ;  suction  is  thus  produced  at  the 
point  of  the  glass  tube  in  the  candle-flame,  and  some  portion 
of  the  gases  and  vapours  is  thus  drawn  from  the  flame  into 
the  cylinder.  As  the  process  continues  the  flame  becomes 
conspicuously  smaller,  because  we  are  removing  part  of  the 
material  which  feeds  it.  It  is  necessary  to  suck  gently  to 
avoid  getting  air  into  the  cylinder  along  with  the  vapours 
from  the  flame.  When  the  cylinder  is  filled  with  the  gases 


1 8  CHEMISTRY  IN   DAILY  LIFE 

from  the  flame,  the  cork  is  removed,  and  a  light  is  brought  to 
the  mouth  of  the  cylinder  ;  the  contents  of  the  cylinder— that 
is  to  say,  the  gas  derived  from  the  candle — take  fire  and  burn 
quietly.  This  experiment  furnishes  a  proof  of  the  justness  of 
the  statement  made  at  the  beginning  of  this  lecture. 

Let  us  now  get  some  fuller  knowledge  respecting  the  three 
chief  materials  used  for  lighting  purposes.  These  three  sub- 
stances are  candles,  oil,  and  coal-gas.  We  shall  not  concern 
ourselves  with  electricity  as  a  source  of  light,  as  this  has 
nothing  to  do  with  chemistry  so  far  as  that  subject  interests 
us  at  present. 

Candles  represent  the  solid  form  of  light-giving  materials. 
In  the  older  days  candles  were  prepared  by  melting  tallow 
(or  crude  animal  fat)  in  a  vessel,  and  dipping  wicks  into  the 
melted  substance.  By  repeatedly  dipping  in  the  same  wick 
the  tallow  candle  was  formed.  These  candles  burnt  very 
imperfectly ;  the  ends  of  the  wicks  required  to  be  constantly 
removed  by  snuffers,  a  kind  of  scissors  which  has  already 
passed  almost  out  of  remembrance.  A  glance  at  the  tallow 
candle  which  was  lighted  at  the  beginning  of  the  lecture  will 
show  the  mode  of  burning  of  these  candles  (compare  fig.  9). 
The  reason  of  the  imperfect  burning  of  these  candles  was  as 
follows.  We  know  that  the  tallow  is  volatilised  by  the  high 
temperature  of  the  flame  ;  this  volatilisation  of  course  takes 
place  from  the  wick,  which  sucks  up  the  fat  that  is  melted  in 
contact  with  it  where  the  flame  produces  heat  sufficient  to 
cause  the  volatilisation  ;  the  gases  thus  produced  make  their 
way  into  the  air,  and  are  burnt  there  by  the  aerial  oxygen, 
which  converts  the  carbon  into  carbonic  acid  and  the  hydrogen 
into  water.  The  wick  itself  does  not  come  into  contact  with 
the  air,  as  the  ascending  gases  cut  it  off  therefrom  ;  the  wick 
is  therefore  carbonised  by  the  heat,  because  the  carbon  of  the 


CANDLES 


wick  cannot  burn  for  lack  of  oxygen,  and  after  a  time  the 
carbonised  end  of  the  wick  prevents  the  flame  from  burning 
symmetrically.  Symmetrical  burning  begins  again  when  the 
end  of  the  wick  is  removed,  or,  as  used  to  be  said,  when  the 
candle  is  snuffed. 

All  this  seems  to  us  to-day  rather  unimportant,  as  we  no 
longer  suffer  personally  from  the  inconvenience  of  constantly 
snuffing  our  lights.  Goethe,  however,  could  still  say  in  his 
maxims  in  rhyme  : 

Wiisste  nicht,  was  sie  besseres  erfinden  kcmnten, 
Als  wenn  die  Lichter  ohne  Putzen  brennten. 

And  it  must  surely  have  been  anything  but 
pleasant  to  break  off  one's  reading  of  an 
evening,  perhaps  every  half-hour,  to  snuff 
the  candles,  whose  light  had  sunk  so  low 
that  reading  was  no  longer  possible. 

These  tallow  candles  were  made  from 
natural  fat.  The  chemical  examination  of 
fat,  which  began  to  have  successful  results 
about  the  end  of  the  eighteenth  century,  led  Fig.  9. 

at  last  to  the  stearin  candles  we  use  to-day. 
This  investigation  showed  that  all  fats  which  are  derived  from 
animals  or  plants  can  be  resolved  into  two  main  constituents 
— namely,  into  several  fatty  acids  and  glycerin. 

In  the  fat  of  animals,  in  oxen-fat  for  example,  three 
fatty  acids — called  stearic^  palmitic^  and  oleic  acids — are  found 
in  combination  with  glycerin.  The  two  first-named  acids  are 
solids,  the  third  is  a  liquid  ;  and  the  more  oleate  of  glycerin 
a  fat  contains  the  less  solid  it  is.  Swine-suet  and  goose-suet, 
for  instance,  are  very  rich  in  the  last-named  substance.  Fat 
is  easily  split  up  into  its  two  constituents  by  technically 


20  CHEMISTRY   IN   DAILY   LIFE 

applicable  processes,  and  the  mixture  of  the  three  fatty 
acids  thus  obtained  is  freed  from  oleic  acid  as  far  as 
possible  by  pressure.  The  white  cake  which  remains  is 
further  purified,  and  from  this  stearin  candles  are  made. 
Before  melting  and  running  into  the  form  of  candles, 
10  per  cent,  of  paraffin — we  shall  learn  immediately  what 
that  is — is  added  to  the  cake,  and  this  produces  the 
homogeneous  white  wax  we  commonly  see  in  stearin  candles. 
A  mixture  of  stearic  and  palmitic  acids  without  this  addition 
crystallises  easily  as  it  cools,  and  candles  made  from  such 
a  mixture  show  a  certain  streakiness,  which  is  prevented 
by  the  addition  of  paraffin. 

The  wick,  round  which  the  mixture  is  poured  in  making 
the  candles,  is  tightly  twisted  on  its  axis,  and  this  twist 
remains  when  the  material  hardens  ;  the  result  is  that  when 
the  candle  is  gradually  consumed,  after  it  has  been  lighted, 
the  wick  is  always  bent,  and  by  this  means  the  end  of  the 
wick  is  constantly  and  automatically  kept  out  of  the 
flame.  Now  there  is  sufficient  oxygen  outside  of  the  flame 
to  insure  the  complete  combustion  of  the  wick,  and  in  this 
way  an  unburnt  head  never  gets  formed,  snuffing  is  not 
needed,  and  stearin  candles  burn  perfectly  symmetrically. 
This  artifice  could  not  be  applied  to  tallow  candles,  because 
the  material  of  which  they  were  made  was  too  soft  to 
maintain  the  necessary  twist  in  the  wick. 

We  must  also  make  mention  of  wax  candles.  Bees'-wax, 
which  is  an  animal  fat,  is  very  like  other  fats  in  its  chemical 
relations.  This  wax  consists  of  fatty  acids  and  an  alcohol ; 
glycerin  is  also,  chemically,  an  alcohol.  The  fatty  acids 
in  bees'-wax  are  cerotic  and  palmitic  acids  :  they  are  combined 
in  the  wax  with  myricyl  alcohol.  As  bees'-wax  is  harder 
than  tallow,  candles  made  from  that  wax  are  found  to  be 
better  than  those  made  from  tallow. 


COMPOUNDS  OF  CARBON  21 

Olive  oil  and  oil  of  rape-seed  were  the  liquids  most 
commonly  used  as  burning  materials  forty  years  ago ;  wicks 
were  dipped  into  the  oils,  and  they  were  burnt  in  lamps 
adapted  for  the  purpose.  These  oils  are  closely  related 
chemically  to  the  fats  ;  they  consist  of  fatty  acids  and 
glycerin.  The  fatty  acids  present  in  them  in  greatest 
quantity  are  of  course  liquids. 

Petroleum,  which  is  now  much  more  used  than  the  oils 
we  have  been  speaking  of,  is  quite  a  different  substance ; 
it  is  a  mixture  of  hydrocarbons.  As  we  often  find  this 
expression,  mixture  of  hydrocarbons •,  in  the  newspapers,  we 
must  try  to  understand  clearly  what  it  means  ;  for  this 
purpose  we  shall  do  well  to  devote  a  little  time  to  the 
consideration  of  the  chemical  aspects  of  the  matter. 

In  chemistry  one  speaks  of  the  elements.  By  that  term  is 
understood  those  constituents  of  bodies  which  have  not 
been  separated  into  simpler  substances  in  any  of  the  many 
attempts  that  have  been  matle  to  effect  such  separations. 
About  eighty  such  elements  are  known.  Most  of  them 
are  very  rare  ;  only  about  twenty  play  a  part  in  daily  life  ; 
and  the  whole  world  with  which  we  have  ordinarily  to  do 
is  constructed  from  these  few  building  stones.  Hence  we 
should  expect  to  find,  as  indeed  we  do  find,  that  the  variety 
of  their  combinations  is  astonishingly  great. 

Now  carbon  is  the  element  which  far  surpasses  all  the 
others  in  its  power  of  forming  combinations ;  the  variety 
of  ways  wherein  atoms  of  carbon  are  able  to  combine  with 
the  atoms  of  other  elements,  or  with  other  atoms  of  carbon, 
is  greater  than  the  ways  of  combination  of  all  the  other 
elements  taken  together.  And  when  nature  created  living 
things  she  made  use  of  carbon.  Therefore  it  follows  that 
carbon  is  present  in  every  substance  which  is  connected  with 


22  CHEMISTRY   IN    DAILY  LIFE 

the  existence  of  life  ;  be  it  the  seed  of  an  apple,  or  the 
flesh  or  the  bony  skeleton  of  an  animal,  all  are  interpenetrated 
with  compounds  of  carbon. 

The  quite  innumerable  number  of  carbon  compounds  may 
be  brought  into  an  easily  comprehended  system  by  making 
the  compounds  with  hydrogen  the  starting-point  of  the 
complete  scheme.  One  atom  of  carbon  is  able  to  bind  to 
itself  four  atoms  of  hydrogen ;  or,  as  is  commonly  said, 
the  atom  of  carbon  is  tetravalent.  This  may  be  represented 

as  follows : 

Hydrogen 

Hydrogen — Carbon — Hydrogen 

I 
Hydrogen 

Now  we  have  already  mentioned  that  carbon  atoms  are 
able  to  form  connected  chains  with  one  another  ;  and  this 
leads  to  the  formation  of  new  hydrocarbons,  in  which  the 
carbon  atoms  are  held  together,  besides  being  in  combination 
with  atoms  of  hydrogen.  Thus  : 

Hydrogen  Hydrogen  H    H    H 

II  III 

Hydrogen— Carbon— Carbon— Hydrogen  ;    or   H— C— C— C— H 

Hydrogen  Hydrogen  H    H    H 

In  these  instances  we  have  connected  together  as  many  as 
three  atoms  of  carbon  ;  and  we  may  go  further — these  chains 
have  been  formed  with  sixty  atoms  of  carbon.  Such  rows 
of  atoms  may  ramify  in  the  most  different  directions  ;  the 
carbon  chains  may,  indeed,  return  upon  themselves  in  the 
form  of  rings— with  which  we  shall  have  to  deal  in  the  last 
lecture,  where  some  of  the  more  recently  introduced  thera- 
peutic agents  will  be  considered.  It  is  very  evident,  then, 
that  the  number  of  possible  hydrocarbons  is  immense. 

In  representing  the  three  hydrocarbons  referred  to  abc 


CHEMICAL  FORMUL/E  23 

we  began  by  writing  the  names  of  the  elements  in  full,  and 
then  we  shortened  these  names  by  using  only  the  initial 
letters  of  them  without  interfering  with  the  intelligibility  of 
the  chemical  formula  of  the  compounds ;  for  the  way  of 
writing  the  third  hydrocarbon  is  indeed  an  actual  chemical 
formula.  The  letter  C  stands  for  carbon,  and  H  for 
hydrogen ;  and  these  letters  are  used  as  the  symbols  for 
those  elements  in  all  languages.  Employing  these  symbols, 
and  adopting  the  same  method  of  representation  as  before, 
we  have  the  following  formulae  for  the  three  hydrocarbons, 
which  are  the  formulae  in  common  use  in  the  chemical 
text-books : 

H  H    H  H    H    H 

I  II  III 

H— C— H  H— C— C— H  H— C— C— C— H 

I  II  III 

H  H    H  H    H    H 

Methane  Ethane  Propane 

American  petroleum  contains  many  hydrocarbons  with 
" single  chains  of  carbon  atoms"  belonging  to  that  series  the 
initial  members  of  which  we  have  here  formulated,  and  the 
technical  names  of  which  we  have  given. 

The  first  member  of  this  series  is  a  gas ;  it  contains  much 
hydrogen,  which  is  the  lightest  element  known.  This 
hydrocarbon  is  formed  in  the  decay  of  vegetable  matter  in 
presence  of  much  water  ;  it  is  found,  therefore,  in  the  gases 
arising  from  marshy  places,  and  for  this  reason  it  is  called 
marsh-gas*  Chemists  give  to  it  also  the  name  methane. 

The  collection  of  this  gas  from  a  marsh  is  an  easier  matter 

*  It  appears,  from  a  letter  of  the  celebrated  French  naturalist  Volta  to 
a  French  scientific  friend,  that  Volta  knew  in  1776  that  every  marsh  gave 
off  this  gas,  or,  as  we  might  say  to-day,  was  a  kind  of  gas  factory.  The 
term  volt,  applied  to-day  to  the  pressure  of  an  electric  current,  is  derived 
from  the  name  of  the  Italian  naturalist ;  as  the  term  ampere  used  in 
measuring  the  quantity  of  the  current,  recalls  the  French  physicist  of 


24  CHEMISTRY   IN    DAILY    LIFE 

than  one  might  be  ready  to  suppose.  It  is  only  necessary 
to  sink  a  large  funnel  in  the  marsh,  with  the  wider  open  end 
downwards ;  the  gas  then  collects  in  the  funnel,  and  bubbles 
upwards,  and  it  may  be  collected  in  a  suitable  apparatus 
connected  with  the  narrow  end  of  the  funnel. 

The  second  hydrocarbon,  ethane,  whose  molecule  contains 
six  atoms  of  hydrogen,  is  a  gas  ;  as  is  also  the  third,  propane, 
which  contains  eight  atoms  of  hydrogen.  This  third  hydro- 
carbon is  found  dissolved  in  crude  petroleum. 

Before  proceeding  further  we  must  give  some  explanation 
of  the  term  molecule,  which  has  just  been  employed.  The 
word  molecule  is  applied  to  the,  hypothetical,  smallest  parts 
of  bodies  which  exhibit  the  properties  that  characterise  these 
bodies.  But  we  are  obliged  to  think  of  molecules  as  capable 
of  being  separated  into  smaller  portions  of  matter,  and  to 
these  fractions  of  molecules  we  give  the  name  atoms.  A 
molecule  is  composed  of  atoms  which  may  be  all  of  one 
kind,  or  of  different  kinds ;  in  the  former  case  we  have  the 
molecule  of  an  element,  in  the  latter  we  have  the  molecule 
of  a  compound. 

When  we  come  to  that  hydrocarbon  which  contains  four 
atoms  of  carbon,  we  find  that  it  is  a  liquid  ;  a  liquid,  it  is 
true,  which  boils  at  i°  C.  [33-8°  F.].  In  keeping  with  this,  it  is 
found  that  the  greater  the  number  of  carbon  atoms  in  the 
molecule  of  a  hydrocarbon  the  higher  is  the  boiling-point  of 
the  compound  ;  for  instance,  kexane,  a  hydrocarbon  with  six 
carbon  atoms,  found  in  petroleum,  boils  at  70°  C.  [158°  F.]. 

that  name.  These  terms  are  constantly  heard  since  the  introduction  of 
electric  lighting.  Accurate  analyses  of  marsh-gas,  on  which  we  base 
the  statement  that  it  consists  of  four  atoms  of  hydrogen  combined  with 
a  single  atom  of  carbon,  were  carried  out  about  forty  years  after  the 
discovery  of  the  gas. 


DISTILLATION  25 

As  the  quantity  of  carbon  increases  the  compounds  become 
less  fluid,  and  at  last  even  solid. 

Large  quantities  of  hydrocarbons  are  present  in  crude 
petroleum.  When  this  is  distilled,  that  is,  is  heated  so  that 
whatever  is  volatilised  at  the  higher  temperature  is  again 
cooled  by  means  of  a  condensing  arrangement  and  is  then 
again  liquefied — somewhat  in  the  manner  shown  in  fig.  10 — 


Fig.  10. 

The  distillation  apparatus  presented  here  is  that  commonly  used  in 
laboratories.  The  liquid  is  heated  to  boiling  in  a  flask,  H,  and  the  vapour 
which  rises  from  the  boiling  liquid  passes  through  the  side-tube,  sealed 
on  to  the  neck  of  the  flask,  into  the  condensing  tube,  A,  which  passes, 
through  the  corks,  c,  into  a  wider  tube,  B,  through  which  a  stream  of 
cold  water  is  kept  constantly  passing  by  means  of  the  rubber  tubing, 
D  and  E.  The  vapour  is  thus  cooled,  and  in  consequence  of  this  it 
becomes  liquid  again,  and  finds  its  way  in  drops  into  the  receiver,  K.  A 
thermometer  fastened  into  the  neck  of  the  distilling-flask  serves  to 
determine  the  temperature  whereat  the  distillation  is  proceeding.  The 
apparatus  used  in  manufactories  is  made  of  metal,  and  is  of  course 
larger,  but  the  principle  is  the  same. 


26  CHEMISTRY   IN    DAILY   LIFE 

the  gaseous  compounds  are  first  given  off;  then  come  the 
lower  boiling  portions  which  are  known  commercially  as 
petroleum  ether. 

Petroleum  ether  often  gives  rise  to  explosions ;  the  reason 
of  this  is  as  follows.  The  volatility  of  this  substance  is  so 
great  that  it  very  easily  evaporates  into  the  air — say,  into  the 
air  of  a  room  ;  if  now  this  mixture  of  air  and  hydrocarbon 
vapour  comes  into  contact  with  a  flame,  the  hydrocarbon  is 
burnt,  very  suddenly,  by  the  large  quantity  of  oxygen  present, 
to  carbonic  acid  and  water ;  and  this  sudden  combustion 
is  accompanied  by  an  explosion.  Petroleum  ether  is  often 
used  to  remove  grease  stains,  etc.  ;  it  should  be  handled  only 
in  daylight,  and  as  far  as  possible  near  an  open  window.  As 
the  distillation  of  crude  petroleum  proceeds  the  boiling-point 
gradually  increases  ;  this  is  made  apparent  by  looking  at  the 
thermometer  fixed  in  the  neck  of  the  flask  (see  fig.  10).  At  a 
certain  temperature  the  receiver  is  changed,  and  the  distillate 
is  collected  apart  from  what  has  come  over  before  ;  this 
distillate  is  our  ordinary  petroleum. 

The  laws  of  almost  every  country  demand  that  commercial 
petroleum  shall  fulfil  certain  requirements  as  regards  its 
inflammability,  and  these  requirements  are  such  that  the  risk 
of  explosion  by  the  burning  of  petroleum  in  our  ordinary 
lamps  is  almost  completely  removed.  Before  these  regula- 
tions were  put  into  practice  it  often  happened  that  petroleum 
contained  some  of  what  we  now  call  petroleum  ether,  and 
that  this  volatilised  in  the  reservoirs  of  the  lamps.  As  soon 
as  the  mixture  of  this  vapour  and  the  air  in  the  reservoir 
became  of  the  proper  composition,  it  ignited  at  the  flame 
of  the  lamp,  an  explosion  took  place,  and  the  lamp  was 
shattered. 

Those  portions  of  crude  American  petroleum  which  remain 
when  the  petroleum  oil  is  distilled  off  have  the  consistence  of 


PARAFFIN— OZONE  2/ 

butter  ;  they  are  worked  up  into  vaseline.  The  residues  after 
the  distillation  of  petroleum  oil  from  Caucasian  petroleum 
[and  from  the  oil  obtained  by  distilling  shale]  are  used  as 
lubricating  oils  for  machinery. 

The  substance  already  referred  to  under  the  name  of 
paraffin  is  a  mixture  of  hydrocarbons  which  contain  much 
carbon  in  their  molecules,  and  are  therefore  solids  at  the 
ordinary  temperature.  These  do  not  come  from  petroleum, 
but  from  tar,  a  substance  obtained  by  the  dry  distillation 
of  coal  or  shale — we  shall  consider  this  process  immediately. 
The  industries  based  on  the  distillation  of  coal  and  shale 
are  conducted  on  a  large  scale  in  Mid-Germany  [and  also  in 
Scotland]. 

It  can  readily  be  understood  that  candles  may  be  made  of 
paraffin  only.  But  such  candles  do  not  meet  with  much 
approval,  inasmuch  as  their  transparent  whiteness  is  not  so 
pleasant  to  the  eye  as  the  opaque  white  appearance  of  stearin 
candles,  and  also  because,  if  they  are  as  long  as  stearin 
candles,  they  generally  become  bent,  as  they  burn,  from  their 
own  weight. 

Now  that  the  conceptions  of  the  atom  and  the  molecule 
have  been  explained  it  is  not  difficult  to  understand  more 
fully  than  before  (see  p.  9)  the  nature  of  ozone. 

Ozone  occurs  in  the  atmosphere  along  with  ordinary 
oxygen.  Each  minutest  portion  of  oxygen  in  the  atmosphere, 
each  molecule  of  oxygen,  consists  of  at  least  two  atoms.  We 
must  ascribe  to  all  elements  a  capacity  to  combine  with  other 
elements  ;  otherwise  each  element  would  remain  for  ever  apart 
from  all  the  others,  and  no  compound  of  any  kind  could  be 
produced.  Now  if  elements  (oxygen,  for  instance)  are  found 
free  in  the  atmosphere,  the  striving  of  their  atoms  to  enter 


28  CHEMISTRY   IN    DAILY   LIFE 

into  combination  is  satisfied  by  the  mutual  union  of  atoms  of 
the  same  kind.  Thus  are  produced  the  molecules  of  ordinary 
oxygen,  each  composed  of  two  atoms.  And  it  happens  that, 
under  the  influence  of  electric  sparks,  and  on  a  large  scale 
during  thunderstorms  (and  there  are  also  other  causes  of  the 
occurrence),  three  atoms  of  oxygen  link  themselves  together. 
This  combination  of  three  atoms  is  not,  however,  very  stable, 
and  the  third  atom  is  ready,  when  opportunity  offers,  to  be 
disengaged  and  to  combine  with  atoms  of  other  elements. 
This  modification  of  oxygen,  the  smallest  particle  of  which  is 
composed  of  three  atoms,  is  called  ozone. 

In  speaking  of  materials  used  for  giving   light,  we  now 
come  to  the  consideration  of  coal-gas. 

When  such  a  substance  as  wood,  peat,  or  coal  is  placed  in 
a  closed  iron  tube  like  that  represented  by  A  in  the  figure 
(fig.  11),  and  the  tube  is  heated  very  highly,*  whatever  in  the 
material  is  volatile  at  the  temperature  employed  will  be 
driven  out  and  will  pass  through  the  exit  tube  into  the  vessel 
C.  In  this  process  the  substance  heated  is  said  to  be 
submitted  to  dry  distillation.  Those  portions  of  the  sub- 
stances volatilised  from  the  wood  or  coal  which  are  liquids  at 
the  ordinary  temperature  will  collect,  in  the  form  of  tar  and 
what  is  called  ammonia  water,  in  C,  while  that  which  is 
gaseous  at  the  ordinary  temperature  will  pass  through  D,  and 
will  be  collected  in  the  glass  jar  E,  which  here  serves  as 
a  gasometer.  The  glass  jar  E  may  well  be  called  a  gaso- 
meter, inasmuch  as  our  apparatus  represents,  on  a  small  scale, 
the  main  parts  of  a  gas  manufactory.  In  an  actual  gas-works 
only  gas-coal  is  used  as  the  material ;  and  in  place  of  large 
iron  tubes,  retorts  of  fire-clay  are  employed,  because  these 
better  withstand  the  continued  action  of  the  heating  furnaces. 
*  For  this  purpose  \ve  use  a  long  gas  furnace. 


MANUFACTURE  OF   COAL-GAS  2Q 

One  hundred  kilograms  of  good  gas-coal  yield  from  28,000  to 
30,000  litres  of  gas  weighing  about  18  kilograms,  and  about 
5  litres  of  tar  and  ammonia  water,  while  about  70  to  75  kilos. 
of  coke  remain  in  the  retorts.  [One  ton  of  good  gas-coal 
yields  about  10,000  to  1 1,000  cubic  feet  of  illuminating  gas, 
about  10  to  13  gallons  of  gas-liquor,  and  from  1,000  to  1,500 
Ibs.  of  coke.] 

On  the  large  scale  the  tar  is  got  rid  of  by  cooling — the 
flask  C  fulfils  this  purpose  in  our  small-scale  experiment ; 
after  this  the  gas  is  brought  into  contact  with  water — it 


Fig.  ii. 

is  washed,  as  the  expression  goes.  Those  constituents  of  the 
gas  which  are  soluble  in  water  are  thus  removed.  The  most 
important  of  these,  so  far  as  quantity  goes,  is  ammonia  ;  were 
this  allowed  to  remain  in  the  gas  the  quality  of  the  gas  would 
be  deteriorated. 

Ammonia  gas  is  composed  of  nitrogen  and  hydrogen  ;  these 
elements  are  present  in  gas-coal  in  the  form  of  very  complex 
compounds,  which  are  decomposed  at  the  high  temperature 
to  which  the  retorts  are  subjected,  with  production  of  the 
simpler  compound  ammonia.  Ammonia  gas  is  very  soluble 


30  CHEMISTRY  IN   DAILY  LIFE 

in  water ;  in  this  dissolved  form  it  is  known  to  every  one  as 
the  very  sharply  smelling  " spirits  of  harts/wrn"  We  shall 
see  later  what  uses  are  made  of  the  large  quantities  of 
ammonia  that  are  obtained  from  the  gas  factories  of  the  world. 

In  the  apparatus  which  we  used  (represented  in  fig.  11)  a 
flask,  D,  was  placed  between  C  and  the  gasometer.  This 
flask  represents  the  vessels  employed  on  the  large  scale  for 
purifying  the  gas  ;  these  are  filled  with  the  purifying  material, 
which  is  for  the  most  part  a  mixture  of  slaked  lime  and 
oxide  of  iron.  The  slaked  lime  serves  to  remove  carbonic 
acid  from  the  gas  by  combining  with  it  to  form  chalk  ; 
the  presence  of  carbonic  acid  cannot  be  prevented  entirely  in 
the  process  of  manufacture.  We  learnt  in  the  first  lecture  to 
use  the  formation  of  chalk  as  a  means  for  detecting  carbonic 
acid  in  expired  breath.  Inasmuch  as  carbonic  acid  is  the 
final  product  of  the  burning  of  carbon,  this  compound  cannot 
itself  be  burnt ;  if,  therefore,  it  is  left  in  coal-gas,  the  gas  is 
thereby  diluted  and  deteriorated.  The  oxide  of  iron  in  the 
purifiers  is  for  the  purpose  of  withdrawing  gaseous  compounds 
of  sulphur  from  the  coal-gas  ;  it  does  this  by  combining  with 
the  sulphur  of  these  compounds  to  form  sulphide  of  iron. 
If  any  sulphur  is  left  in  gas,  this  sulphur  burns,  when  the 
gas  is  lighted,  to  sulphurous  acid,  which  is  a  gaseous  body 
with  a  pungent  smell  well  known  to  every  one  as  the  smell 
of  burning  sulphur;  some  of  the  sulphur  is  also  burnt  to 
sulphuric  acid  at  the  high  temperature  of  the  flame  of  coal-gas. 

These  purifiers  remove  almost  all  the  sulphur  from  the  gas, 
except  that  which  exists  in  the  form  of  a  compound  called 
bisulphide  of  carbon.  The  quantity  of  this  compound  in 
coal-gas  is  extremely  small ;  but  its  complete  removal  on 
the  large  scale  remains  to-day  an  unsolved  problem  of  the 
gas  trade. 

When  the  gas  has  been  purified  in  the  way  described  it  is 


COMPOSITION   OF  COAL-GAS  31 

collected  in  gasometers,  and  it  is  conducted   from  these  in 
pipes  to  the  places  where  it  is  to  be  used. 

The  following  analysis  will  give  an  idea  of  the  composition 
of  coal-gas : 

Hydrogen        45*2  per  cent,  by  volume. 

Methane  (see  p.  23) 35-0        „ 

Other  hydrocarbons 4*4        „  „ 

Carbon  monoxide       8 '6        „  „ 

Carbonic  acid 2*0        „  „ 

Nitrogen  ...       4*8        „  „ 

lOO'O 

When  coal-gas  is  burnt,  carbonic  acid  is  produced  from  the 
carbon,  and  water  from  the  hydrogen,  of  the  gas  ;  on  account 
of  the  high  temperature  the  water  is  produced  in  the  gaseous 
form.  Thus  coal-gas  is  almost  wholly  changed,  by  burning, 
into  two  odourless,  colourless  gases.  Besides  these  gases,  the 
air  of  rooms  wherein  coal-gas  is  burnt  contains  a  little 
sulphurous  acid  gas,  produced  by  the  burning  of  the 
traces  of  sulphur-containing  compounds  in  the  gas.  It 
is  on  account  of  this  sulphurous  acid  gas  that  window 
plants  do  not  flourish  well  in  rooms  wherein  coal-gas  is 
burnt.  The  small  quantities  of  sulphurous  acid  produced 
by  burning  coal-gas  are  found,  fortunately,  to  be  quite 
harmless  to  human  beings. 

It  has  been  said  above  that  part  of  the  sulphur  in  gas  is 
burnt  to  sulphuric  acid.  This  result  of  the  combustion  is 
made  apparent  in  the  spots  that  appear  on  the  globes  of 
gas-lamps  when  these  globes  are  not  very  frequently  cleaned. 
Small  drops  of  liquid  sulphuric  acid  settle  on  the  globes,  and, 
as  sulphuric  acid  is  an  extremely  corrosive,  that  is  destructive, 
substance,  the  particles  of  dust  that  fall  upon  the  globes  are 
charred  by  it.  Hence  it  is  that  the  globes  of  such  lamps  get 
gradually  covered  with  brownish  specks ;  such  specks  are 


CHEMISTRY   IN    DAILY   LIFE 


not  seen  on  the  chimneys  used  on  lamps  for  burning  oil 
or  petroleum,  inasmuch  as  these  substances  do  not  contain 
sulphur. 

What  remains  to  be  said  about  the  nature  of  luminous 
flame  can  now  be  made  clear  and  illustrated  very  conveniently 

in  connection  with  the  flame 
of  coal-gas. 

The  presence  of  carbon  in 
the  luminous  flame  is  demon- 
strated by  holding  a  porce- 
lain plate  in  the  flame,  when, 
on  account  of  the  cooling 
effect  of  the  cold  surface, 
carbon  is  deposited  on  the 
plate  in  the  form  of  soot. 
This  carbon  was  separated 
in  the  flame  itself  by  the  heat 
of  the  flame ;  and  as  at  the 
same  time  it  was  raised  to  a 
white  heat  it  caused  the 
luminosity  of  the  flame. 
When  this  carbon  reaches 
the  edge  of  the  flame  and 
there  comes  into  contact  with 
the  oxygen  of  the  air,  it  is 
burnt  to  carbonic  acid,  and 

in  this  form  it  escapes  into  the  surrounding  atmosphere.  It 
can  easily  be  shown  that  this  is  actually  what  occurs.  Those 
of  you  who  cook  by  gas — a  method  which  is  rightly  coming 
more  and  more  into  use  in  the  kitchen — always  use  non- 
luminous  gas-flames,  which  do  not  cover  the  cooking-vessels 
with  soot  because  no  separation  of  carbon  occurs  in  such 


Fig.  12. 


GAS-COOKING  APPARATUS 


33 


flames.  Chemists  have  employed  gas,  when  it  was  to  be 
obtained,  for  heating  purposes  for  the  last  fifty  years ;  they 
make  use  of  the  burner  invented  by  Bunsen,  which  burner 
has  of  late  years  been  adapted  to  apparatus  for  cooking  by 
gas  (see  R,  fig.  12).  In  a  Bunsen  burner  the  gas  issues  from 
a  narrow  opening  (C,  fig.  12).  If  it  is  lighted  at  this  opening 
the  gas  burns  with  the  ordinary  luminous  flame ;  but  if  there 
is  placed  over  this  opening  a  tube  with  holes  for  admitting 
air  near  to  the  opening  from  which  the  gas 
issues  (see  D,  E,  F,  fig.  12),  the  gas  streaming 
through  this  tube  is  able  to  carry  a  little  air 
with  it.  If  we  now  light  the  gas  at  the  open 
end  of  the  tube  the  flame  is  non-luminous, 

|ji(!iil:,i;'i!; 

because  there  is  so  much  air  mixed  with  the 
gas  that  the  oxygen  in  this  air  suffices  to  cause 
combustion  of  all  the  carbon  in  the  gas ;  at 
the  same  time,  a  great  heating  effect  is  pro- 
duced. If  the  holes  in  the  tubes  are  closed  by 
turning  the  short  outer  tube  (H,  fig.  12),  the 
flame  burns  luminously,  as  we  should  expect. 

The  arrangement  in  all  gas-cooking  apparatus 
is  exactly  similar  to  that  used  in  the  Bunsen 
burner.  You  see  that  the  gas  issues  from  a 
small  opening  immediately  in  front  of  the  Fi£-  J3- 

stop-cock,  and  near  this  you  see  several  open- 
ings for  the  entrance  of  air  into  the  wider  tube  which 
conducts  the  mixture  of  gas  and  a  little  air  to  the  place 
where  it  is  to  be  burnt.  Should  too  much  air  get  into 
the  tube  by  accident  we  should  have,  of  course,  an  explosive 
mixture  ;  were  this  ignited  the  gas  would  burn  for  a  moment, 
and  the  flame  would  then  strike  back  to  the  opening  by 
which  the  coal-gas  enters  the  tube,  where  it  would  burn, 
as  at  this  point  it  would  come  into  contact  with  the 
3 


34  CHEMISTRY  IN   DAILY  LIFE 

external  air,  which  would  still  be  needed  to  maintain  the 

combustion. 

As  has  been  already  indicated,  a  non-luminous  gas-flame 

gives  out  very  much  heat,  because  of  the  rapid  combustion 

that  is  proceeding  in  it.     If  we  hold  a  bundle  of  platinum 

wires  in  such  a 
A  flame,  the  platinum, 
which  is  not  itself 
in  the  least  changed 
at  this  temperature, 
becomes  heated  to 
full  redness  and 

Fig.  14. 

radiates  light.    The 

latest  important  advance  made  in  lighting  by  gas — namely, 
the  incandescent  gas-light — exhibits  this  process  in  a  very 
complete  way.  In  the  incandescent  gas-light  (see  fig.  13), 
the  flame  is  rendered  non-luminous  by  the  admission  of  air, 
in  the  same  way  as  in  the  Bunsen  burner.  We  always 
notice  several  small  openings — generally  four — in  these  in- 
candescent lamps,  placed  near  the  point  where  the  gas  enters 
the  burner.  The  very  hot,  non-luminous  flame  heats  a  hollow 
mantle  suspended  in  it  to  a  very  high  temperature.  This 
mantle  is  saturated  with  certain  oxides,  partly  the  oxides  of 
rare  elements  such  as  oxides  of  cerium  and  thorium,  which  have 
long  been  known  to  emit  very  clear  light  when  they  are  heated. 
Auer  was  the  first  to  turn  this  property  successfully  to 
account  in  daily  life.  He  busied  himself  with  the  matter  for 
a  longtime.  So  long  ago  as  1885  he  had  constructed  an  in- 
candescent lamp  for  lighting  rooms  ;  but  the  lamp  was  made 
serviceable  only  in  October  1891,  and  since  that  time  it  has 
been  much  improved  by  him,  especially  by  so  mixing  the 
most  appropriate  oxides  in  the  mantle  as  to  produce  a  white 
light  pleasant  to  the  eyes,  in  place  of  the  somewhat  faded, 


THE   ELECTRIC  FURNACE  35 

moonshiny  colour  which  the  light  possessed  when  it  was  first 
introduced. 

Daily  experience  shows  us  that  high  temperatures  have 
different  effects  on  different  substances.  Since  we  have  been 
able  to  command  very  high  temperatures,  it  has  become 
possible  to  prepare  many  compounds  which  could  formerly 
be  obtained  with  great  difficulty,  or  not  at  all.  Temperatures 
higher  than  any  formerly  known  are  reached  between  the 
carbon  points  of  the  electric  arc-lamp.  When,  for  example,  a 
mixture  of  charcoal  and  chalk  is  brought  into  the  electric  arc 
— the  apparatus  is  called  an  electric  furnace  (see  fig.  15) — a 

'•v  \fV\\ 

o#W) 


l 


Fig-  15- 

reaction  happens  between  the  two  substances,  and  a  new 
substance  called  calcium  carbide  is  produced.  This  substance 
—it  was  first  prepared  in  quantity  by  Moissan — is  very  stable 
towards  heat,  but  it  readily  reacts  with  cold  water  and 
produces  a  gas,  which  has  been  known  for  a  long  time,  and 
is  called  acetylene.  This  gas,  which  used  to  be  costly,  is  now 
produced  at  so  cheap  a  rate  that  it  is  used  for  lighting  purposes. 
By  burning  acetylene  in  oxygen,  in  a  specially  constructed 
burner,  shown  in  fig.  14  (acetylene  enters  at  C,  and  oxygen  at 
B,  and  the  mixture  is  burnt  at  A),  an  exceedingly  hot  flame 
is  obtained  ;  this  flame  is  used  for  firmly  joining  sheets  of  iron 
without  solder.  The  flame  is  run  along  the  edges  of  the  plates, 
the  iron  melts,  and  a  compact  homogeneous  plate  is  produced. 


LECTURE    III 

Food  of  Plants— Manuring— Fallow  land— Artificial  manures— Bones 
— Superphosphates — Potash  salts — Manuring  with  nitrogen — 
Bases,  acids,  and  salts — Mother-liquor — Food  of  men  and  animals 
— Experiments  on  digestion — Albuminoids — Fats — Carbohydrates — 
Milk  and  its  coagulation— Cheese — Soxhlet's  extraction  apparatus — 
Fibrin — Serum — Artificial  Fodder — Gelatin. 

WE  come  now  to  food-stuffs. 

The  surface  of  the  earth  whereon  plants  and  animals  live 
consists  of  lifeless  materials.  Plants  are  able  to  take  all  that 
they  require  for  their  life  from  this  lifeless  matter  which  forms 
the  surface  of  the  earth.  Animals  cannot  do  this,  and  they 
are  dependent,  directly  or  indirectly,  on  plants  for  their 
nourishment.  A  tree,  for  instance,  stands  in  the  same  place 
for  hundreds  of  years,  and  nature  supplies  it  with  all  that  is 
needed  for  its  existence  ;  rain  brings  the  moisture  the  tree 
requires,  and  the  carbon  which  it  needs  for  forming  wood  and 
all  that  complex  structure  which  renders  its  life  possible  it 
takes  chiefly  from  the  carbonic  acid  of  the  air.  The  leaves 
of  plants,  and,  in  all  probability,  more  especially  the  green 
parts  of  the  leaves,  which  are  called  chlorophyll-grains,  have 
the  power  of  decomposing  carbonic  acid,  which  itself  consists 
of  carbon  and  oxygen,  in  such  a  way  that  the  leaves  make 
use  of  the  carbon  and  give  out  the  oxygen.  This  is  the  more 
remarkable  as  carbonic  acid  is  a  very  stable  gas,  which  can 
be  separated  into  its  constituents  in  the  laboratory  only  with 

36 


FOOD  OF   PLANTS  37 

difficulty,  and  is  itself  produced,  as  we  know,  at  the  high 
temperature  of  burning  flames. 

The  soil  whereon  the  plant  grows  furnishes  the  other 
inorganic  compounds — that  is  to  say,  the  compounds  derived 
from  lifeless  matter— that  are  required  by  the  plant.  We  are 
enabled  to  see  these  compounds  by  burning  the  plant — wood, 
for  instance — when  they  remain  as  ashes. 

If  we  examine  such  plant-ashes  more  narrowly,  analyses  of 
them  give  us  the  following  results.  The  quantity  of  ash  of  a 
rye-plant,  for  instance,  when  the  plant  is  in  bloom,  amounts 
to  6*38  per  cent,  of  the  weight  of  the  plant  ;  the  ash  of  ripe 
rye-grains  amounts  to  1*93  per  cent.  The  ash  itself  has  the 
following  percentage  composition — we  shall  here  employ  the 
most  simple  designations  we  can. 

COMPOSITION  OF  THE     COMPOSITION  OF  THE 

ASH  OF  RYE-PLANTS.     ASH  OF  RYE-GRAINS. 

Per  cent.  Per  cent. 

Potash  salts 37'i6  34'5° 

Common  salt 076  0*90 

Oxide  of  iron 0*50  0*20 

Lime  and  magnesia  ...         ...  I2'32  ...         ...  14'ij 

Phosphoric  acid         20*35  47*52 

Sulphuric  acid           4x53  

Silica 24-88  275 

lOO'OO  lOO'OO 

All  these  things  must  be  contained  in  the  soil  if  such  a 
plant  as  rye  is  to  thrive  thereon.  There  is  never  any  lack  of 
some  of  these  constituents,  such  as  silica,  which  is  the  chemical 
name  for  pure  sand,  and  oxide  of  iron.  On  the  other  hand, 
investigations,  the  consequences  of  which  were  fully  elucidated 
for  the  first  time  by  Liebig,  have  taught  us  to  recognise  that 
unless  the  soil  is  to  become  exhausted  we  must  add  to  it 
pJw  spheric  acid,  potash  salts,  and  nitrogen. 

We  have  not  as  yet  become  acquainted  with  the  last  of 
these  substances  in  this  connection,  but  we  shall  get  to  know 


38  CHEMISTRY   IN    DAILY   LIFE 

something  about  it.  When  we  consider  that  all  the  civilised 
peoples  of  whom  we  know  anything  have  practised  agri- 
culture from  the  earliest  times,  and  further,  when  we  think 
that  Liebig  was  the  first,  in  the  forties  of  last  century,  to  make 
clear  what  part  the  soil  has  to  play,  we  must  certainly  be 
astonished  that  such  an  immense  time  was  needed  for  man- 
kind to  come  to  this  knowledge,  and  we  must  the  more 
admire  Liebig  when  we  consider  that  at  no  time  of  his  life 
was  he  a  farmer.  Even  Thaer,  who  was  the  great  reformer 
of  agriculture,  and  was  the  first  to  endeavour  in  a  serious 
way  to  place  this  industry  on  a  scientific  foundation,  and  who 
indeed  obtained  very  remarkable  results  about  the  beginning 
of  last  century — even  Thaer  regarded  the  ash-contents  of  the 
plant  as  only  casual  constituents.  According  to  him  plants 
flourish  the  better  the  deeper  is  the  layer  of  humus  in  the 
soil ;  he  arrived  at  quite  a  false  conception  of  the  state  of 
affairs  regarding  the  nourishment  of  plants.  It  may  be  said 
without  exaggeration  that  until  Liebig  discovered  the  essential 
facts  all  agriculture  had  been  merely  a  robbing  of  the  soil, 
whereby  in  the  course  of  time  many  parts  of  the  earth  had 
been  utterly  exhausted, 

The  observation  was  made  at  a  very  early  period  that  if 
the  same  crop  is  taken  from  the  same  plot  of  ground  for 
several  years  in  succession  the  yield  gradually  diminishes  ; 
and  for  this  reason  the  cultivation  of  crops  has  always  been 
alternated  in  a  certain  cycle. 

Thus  we  find  that  the  books  on  agriculture  which  have 
come  down  to  us  from  the  ancient  classical  times  recommend 
a  rotation  of  crops  ;  and  the  works  on  agriculture  which  were 
written  before  the  time  of  Frederick  the  Great  contain 
essentially  nothing  that  is  not  to  be  found  in  these  ancient 
writings.  We  can  scarcely  speak  of  progress  in  agriculture 
during  these  ages. 


ROTATION  OF  CROPS— FALLOW  39 

The  reason  of  the  increased  productiveness  insured  by 
practising  a  rotation  of  crops  lies  in  this,  that,  because  the 
composition  of  the  ashes  of  the  various  plants  is  not  the  same, 
so  the  exhaustion  of  the  soil  does  not  take  place  in  the  same 
direction  in  every  year.  On  the  other  hand,  fields  have  been 
manured  since  ancient  times  with  the  waste  products  at  the 
disposal  of  the  farmer,  so  that,  without  exactly  knowing  why, 
what  had  been  taken  from  the  soil  was  returned  to  it,  and  the 
productiveness  of  the  soil  was  thereby  found  to  be  improved. 
But,  as  much  of  the  produce  of  the  farm  is  sold,  a  certain 
quantity  of  the  inorganic  salts  will  be  removed  annually  from 
the  soil  without  being  returned  thereto,  and  for  this  reason  a 
diminution  in  the  fertility  of  the  soil  must  take  place,  notwith- 
standing the  manuring  to  which  the  soil  is  subjected.  Ordi- 
nary experience  proved  this  to  be  the  case,  but  no  one  was 
able  to  find  the  true  explanation. 

This  leads  us  to  the  so-called  fallow  system  of  farming. 
When  fields  had  borne  crops  for  some  years  they  were  allowed 
to  remain  for  a  year  uncultivated,  and  this  had  a  real  effect  in 
increasing  their  fertility  afterwards.  Why  this  should  be  so 
cannot  be  understood  without  further  explanation.  For,  if 
one  may  put  it  in  this  way,  neither  phosphoric  acid  nor  potash 
salts  are  rained  from  the  heavens,  and  none  of  these  salts 
comes  into  the  soil  from  the  outside  by  letting  that  soil  lie 
fallow  ;  no  improvement  of  the  soil  takes  place  in  this  way. 

The  good  results  of  the  system  of  fallow  depend  on  the 
following  considerations.  The  greater  part  of  the  phosphoric 
acid  and  of  the  potash  salts  in  the  soil  is  present  as  compounds 
insoluble  in  water.  Such  insoluble  substances  cannot  be 
made  use  of  by  the  roots  of  the  plants,  as  these  are  only  able 
to  absorb  substances  in  solution.  Now  the  moisture  in  the 
soil,  together  with  the  carbonic  acid  circulating  therein,  which 
is  derived  from  the  air,  seize  on  these  insoluble  compounds 


40  CHEMISTRY   IN    DAILY    LIFE 

and  change  them  into  soluble  substances.  If,  then,  the  store 
of  material  that  has  thus  been  made  available  for  the  nourish- 
ment of  plants  is  not  withdrawn  from  the  soil  for  a  year,  this 
store  suffices,  along  with  that  which  is  dissolved  every  year, 
to  make  it  possible  after  a  time  to  reap  a  profitable  harvest. 

It  was  discovered  about  the  year  1750  that  the  fields  might 
be  sown  with  clover  in  the  year  in  which  they  had  until  then 
been  allowed  to  lie  fallow  without  any  noticeable  diminution 
in  the  yield  when  corn  was  afterwards  raised.  What  was  for 
that  period  a  great  advance  was  thus  made,  as  more  cattle 
could  now  be  reared,  and  so  more  manure  could  be  obtained 
for  the  ground  ;  and  when  the  soil  became  unsuited  for  grow- 
ing clover,  as  experience  soon  showed  did  occur,  it  was 
possible  to  raise  peas,  beans,  potatoes,  and  the  like.  In  this 
way  arose  a  regular  rotation  of  straw  and  green  crops,  with  a 
periodical  interpolation  of  clover. 

If  the  system  of  fallow  was  not  required,  this  was  only 
because  the  different  crops,  as  has  already  been  pointed  out, 
use  up  very  different  quantities  of  the  particular  inorganic 
food-salts,  so  that,  by  a  judicious  system  of  rotation,  only 
small  quantities  of  those  salts  which  are  much  used  were 
removed  throughout  the  year  by  cropping  the  soil.  But, 
without  being  aware  of  it,  agriculture  committed  a  greater 
robbery  of  the  inorganic  salts  of  the  soil  than  before  ;  for 
in  order  that  one  field  might  be  more  richly  manured  the 
neighbouring  field  was  made  poorer.  The  effects  of  this 
injury  to  the  soil  would  have  become  apparent  in  our  time 
had  not  the  connection  between  the  soil  and  the  crops  been 
made  clear  by  Liebig,  and  had  not  a  cheaper  substitute  for 
the  inorganic  salts  removed  from  the  soil  been  obtained  from 
the  store  that  exists  in  lifeless  materials.  By  this  means  the 
system  of  fallow  was  made  practically  superfluous, 


ARTIFICIAL   MANURES  41 

The  loss  which  the  soil  suffers  by  the  removal  of  the  harvest 
is  made  good  to-day,  in  so  far  as  this  loss  is  not  covered  by 
the  natural  manure,  by  the  addition  of  artificial  manure. 
Indeed,  as  any  quantity  of  artificial  manure  is  at  our  disposal, 
the  productiveness  of  the  soil  can  be  very  much  increased  by 
using  as  much  of  this  manure  as  experience  has  shown  to  be 
expedient.  The  merit  of  Liebig  was  most  conspicuous  in  this 
method,  which  is  the  only  rational  one,  of  giving  back  to  the 
soil,  by  artificial  means,  the  compounds  and  substances  which 
the  growth  of  the  plants  had  withdrawn  from  it.  Hence  it  is 
that  we  have  recourse  nowadays  to  the  chemical  manufactory 
for  the  preparation  of  artificial  manures.* 

The  following  are  the  chief  sources  whence  phosphoric  acid 
can  be  obtained  cheaply — if  the  cost  of  the  phosphoric  acid 
were  great  it  would  be  useless  to  the  farmer. 

First  of  all,  from  bones.  These  consist  for  the  most  part  of 
phosphate  of  lime  ;  besides  this  they  contain  fat  and  gelatinous 
substances.  The  fat  is  extracted  from  bones  nowadays  with 
petroleum  ether,  and  is  used  for  making  candles  and  soap. 

*  Properly  prepared  mixtures,  soluble  in  water,  of  the  foodstuffs  most 
valuable  to  plants,  especially  those  required  by  garden-  and  pot-plants, 
are  now  to  be  had  in  the  market  and  have  come  into  ordinary  use.  In 
using  these  mixtures  for  manuring  plants  in  pots  great  care  must  be  taken 
to  add  the  proper  quantity,  as  the  effect  of  too  much  of  such  mixtures  is 
very  injurious.  About  half  a  gram  of  such  a  mixture  of  food-salts  should 
be  used  for  each  kilo,  of  earth  in  the  pot,  and  this  half-gram  should  be 
dissolved  in  half  a  litre  of  water.  [About  7  grains  per  2  Ibs.  of  earth, 
dissolved  in  a  pint  of  water.]  If  more  concentrated  solutions  than  this 
are  used  the  roots  of  the  plants  are  likely  to  be  corroded,  or  even  killed. 
The  quantity  named  above  should  serve  for  a  year  ;  and  half  of  it  should 
be  applied  each  six  months.  The  quantity  of  food-salts  to  be  used  in  a 
garden  depends  on  the  depth  to  which  the  soil  is  trenched.  If,  for 
instance,  a  square  metre  is  dug  20  centimetres  deep,  then  (using  the  pro- 
portion T  :  2,000)  a  solution  of  100  grams  of  the  soluble  food-salts  should 
be  employed.  [Eleven  square  feet  dug  8  in.  deep  require  a  solution  qf 
3^  oz.  of  the  food-salts.] 


42  CHEMISTRY   IN    DAILY   LIFE 

We  have  already  spoken  of  candles,  and  we  shall  have  some- 
thing to  say  of  soap  later.  The  process  for  the  extraction  of 
gelatin  from  bones  will  not  be  described,  as  the  understanding 
of  it  requires  a  large  amount  of  preliminary  explanation. 

When  bones  are  calcined  in  a  closed  vessel  with  an  exit 
tube  for  the  escape  of  vapour,  similar  to  that  wherein  coal 
is  heated  in  the  manufacture  of  gas,  a  black  mass  is  left 
behind  corresponding  with  the  coke  left  in  the  gas-retorts  ; 
this  black  residue  is  known  as  bone  charcoal  [or  animal 
charcoal].  This  animal  charcoal  possesses  the  property  of 
removing  the  colour  from  coloured  solutions ;  for  instance, 
if  red  wine  is  shaken  with  animal  charcoal  and  then  filtered, 
a  clear,  colourless  liquid,  like  water,  is  obtained.  This 
property  of  animal  charcoal  is  made  use  of  in  many  indus- 
tries ;  for  instance,  sugar-syrup  is  decolourised  by  this 
method.  Blacking  for  shoes  is  made  by  mixing  very  finely 
ground  animal  charcoal  with  some  suitable  kind  of  grease. 

If  bones  are  calcined  in  the  air  the  whole  of  their  carbon 
is  burnt  away,  and  a  white  substance  remains.  Calcined 
bones  form  the  material  from  which  phosphorus  (which  we 
heard  about  in  the  lecture  on  matches)  is  manufactured  ; 
they  are  also  used  in  the  preparation  of  milk  glass  (see 
Lecture  X.). 

Another  source  of  phosphoric  acid  is  the  phosphate  of 
lime  which  is  found  very  widely  distributed  over  the  surface 
of  the  earth.  This  substance,  which  is  known  as  phosphorite, 
contains  varying  quantities  of  impurities.  Large  quantities 
of  phosphorite  are  found  in  Florida,  in  North  America, 
containing  on  the  average  about  82  per  cent,  of  phosphate  of 
lime  ;  and  as  the  impurities  in  the  Florida  phosphorite  do 
not  materially  affect  its  chemical  treatment,  this  American 
phosphorite  finds  a  market  everywhere. 

Guano  was  once  of  much  importance  ;  but  in  consequence 


PHOSPHATES   AS   MANURE  43 

of  the  exhaustion  of  the  deposits  of  this  substance  it 
is  gradually  becoming  less  appreciated.  Guano,  which  is 
the  decomposed  excrement  of  sea-birds,  was  found  in  large 
deposits  on  the  Peruvian  coast  and  the  islands  off  that  coast  ; 
it  is  extremely  rich  in  phosphoric  acid  and  contains  also  much 
nitrogen. 

Finally,  the  dephosphorising  of  iron — a  process  which  will 
be  dealt  with  in  the  eleventh  lecture — produces  a  substance 
known  as  Thomas's  phosphate  powder  [or  basic  slag],  a  name 
derived  from  the  discoverer  of  the  method. 

The  phosphoric  acid  in  these  substances,  with  the  excep- 
tion of  that  in  the  material  last  mentioned  and  part  of 
that  in  guano,  is  contained  in  the  form  of  insoluble  phos- 
phate of  lime,  which  is  also  the  phosphate  present  in  the 
soil. 

When  this  insoluble  phosphate  is  brought  on  to  tilled 
land  in  fine  powder  its  efficiency  is  very  small,  as  it  is 
very  slowly  broken  up  by  the  naturally  occurring  processes 
whereof  we  have  spoken  already.  It  is,  indeed,  almost 
valueless  to  the  farmer,  and  the  plants  bring  it  into  an 
available  form  only  after  the  lapse  of  years.  But  matters 
are  very  different  if  this  phosphate  is  artificially  changed 
into  a  form  which  can  be  easily  and  readily  assimilated 
by  the  roots  of  the  plants.  This  process  of  decomposition 
consisted,  until  the  year  1910,  essentially  in  powdering  the 
phosphate  finely,  and  then  treating  it  with  concentrated  sul- 
phuric acid. 

Most  of  the  phosphoric  acid  in  the  materials  we  have 
mentioned  is  combined  with  lime,  in  the  proportion  of 
three  molecules  of  lime  to  one  molecule  of  the  acid.  Sul- 
phuric acid  is  a  stronger  acid  than  phosphoric ;  but  one 
molecule  of  sulphuric  acid  combines  with  only  one  molecule 
of  lime.  If,  then,  two  molecules  of  sulphuric  acid  are; 


44  CHEMISTRY   IN    DAILY   LIFE 

caused  to  react  with  burnt  bones,  or  mineral  phosphorite, 
a  new  compound  is  obtained  in  which  one  molecule  of  phos- 
phoric acid  is  combined  with  one  molecule  of  lime,  and  at 
the  same  time  two  molecules  of  sulphate  of  lime,  or  gypsum, 
as  it  is  commonly  called,  are  formed.  The  following  scheme 
makes  the  process  more  evident  : 


I  Lime        Sulphuric  acid  ' 
Phosphoric  acid^-Lime  +    Sulphuric  acid  , 
\Lime 

The  phosphate  of  lime  produced  in  this  way  is  soluble  in 
water,  and  is  easily  assimilated  by  plants  when  it  is  brought 
into  the  soil.  It  is  sold  under  the  name  superphosphate. 
When  one  speaks  of  manuring  with  phosphoric  acid  one 
refers  to  this  artificially  prepared  compound  of  phosphoric 
acid  and  lime.  An  aqueous  solution  of  phosphoric  acid  itself 
is  so  corrosive  that  it  would  destroy  all  plant  growth. 

In  order  to  make  superphosphate  it  is  necessary  to  use 
sulphuric  acid,  and  this,  of  course,  means  expenditure  of 
money.  A  cheaper  method  of  making  superphosphate  has 
been  sought  for  during  the  last  fifty  years.  A  process  intro- 
duced in  1910  by  a  Norwegian  named  Palmaer  for  setting 
free  the  phosphoric  acid  in  phosphorite  seems  to  have  be- 
come a  serious  competitor  against  the  older  method.  Sodium 
chloride  is  the  name  given  by  chemists  to  common  salt, 
because  it  is  a  compound  of  sodium  and  chlorine  ;  when  an 
electric  current  is  passed  through  an  aqueous  solution  of  this 
compound,  under  certain  definite  conditions,  chlorate  of  soda 
is  formed.  (For  some  account  of  the  chemical  action  of  the 
electric  current  see  Lectures  IX.  and  XI.)  Chlorate  of  soda 
can  be  separated  by  the  current  into  soda  and  chloric  acid, 
which  can  be  kept  apart.  Phosphorite  dissolves  when  it  is 


PHOSPHATES  AS   MANURE  45 

brought  into  the  solution  of  chloric  acid.  If  the  soda  is  now 
added  to  this  acid  solution  of  phosphate  of  lime,  the  free  acid 
is  neutralised,  and  the  phosphate  of  lime  is  thrown  down  as 
a  fine  powder,  that  is,  in  a  condition  eminently  suited  for  use 
as  a  plant-manure.  The  liquid  that  is  filtered  from  the 
precipitated  phosphate  contains  only  chlorate  of  soda.  This 
liquid  is  again  decomposed  electrolytically,  and  the  products 
— soda  and  chloric  acid — are  separated  ;  a  fresh  quantity  of 
crude  phosphorite  is  added  to  the  chloric  acid,  and  so  the 
process  is  made  continuous.  The  solution  of  chlorate  of  soda 
is  used  again  and  again  for  making  fresh  quantities  of  phos- 
phate manure  ;  there  is  no  waste  of  material  except  such 
loss  as  is  inevitable  in  the  process  of  manufacture.  In  place 
of  the  cost  of  sulphuric  acid  used  in  decomposing  the  crude 
phosphate,  there  is  the  smaller  cost  of  the  electrolytic  plant  ; 
not  to  mention  other  advantages  which  must  be  taken  into 
account,  such  as  the  possibility  of  using  phosphorite  which 
could  not  profitably  be  treated  by  the  older  process,  because 
of  the  impurities  in  it  that  would  use  up  much  sulphuric 
acid. 

A  word  must  still  be  said  regarding  the  Thomas 's phosphate 
powder.  This  substance  contains  a  phosphate  of  lime 
which  can  be  assimilated  by  plants  without  any  preliminary 
treatment  with  sulphuric  acid.  As  no  money  need  be  spent 
in  artificially  decomposing  this  substance,  the  Thomas's 
phosphate  is  a  very  cheap  source  of  phosphoric  acid  ;  it  is 
much  used  for  manuring  meadow-land,  for  which  purpose  it 
is  particularly  suitable. 

We  come  now  to  the  consideration  of  potash  salts  as 
manuring  material.  Potash  salts  were  very  expensive  until 
about  the  year  1860.  Potashes,  known  in  chemical  language 
as  carbonate  of  potash,  was  the  only  form  in  which  potash 


46  CHEMISTRY  IN   DAILY  LIFE 

came  into  the  market.  As  the  name  indicates,  potashes 
was  originally  prepared  by  boiling  plant-ashes  with  water 
in  pots.  It  was  much  used  in  manufactures  (glass  making, 
soap  making,  dyeing,  etc.) ;  as  the  price  was  very  high,  and 
indeed  continues  high  although  it  is  now  made  from  other 
salts  of  potash,  it  could  never  come  into  use  as  a  material  for 
manuring.  In  a  later  part  of  these  lectures  we  shall  consider 
this  substance  in  more  detail  in  connection  with  soda.  All 
the  other  inexpensive  potash  salts  in  use  to-day  as  manures 
are  obtained  from  the  salt  mines  in  the  neighbourhood  of 
Stassfurt,  near  Magdeburg. 

There  were  many  salt-springs  in  Stassfurt  that  became 
exhausted  during  the  last  centuries.  The  exhaustion  of  these 
springs  led  to  attempts  to  get  rock-salt  by  boring  in  that 
neighbourhood.  The  boring  brought  up  a  kind  of  salt  which 
tasted  bitter ;  large  quantities  of  this  were  thrown  aside 
under  the  name  of  Abraum  sals  (useless  salt),  when  pure 
rock-salt  began  to  be  obtained  by  mining. 

These  bitter  salts  are  nothing  else  than  salts  of  potash  ; 
and  the  immense  deposits  of  such  salts  have  caused  a  great 
industry  to  spring  up  in  that  neighbourhood  whereby 
agriculturists  all  over  the  world  are  supplied  with  potash. 
It  is  necessary  to  work  up  the  natural  raw  salts  in  manu- 
factories in  order  to  produce  a  material  suitable  for  use  as  a 
manure.  Some  of  the  bye-products  of  this  manufacture  are 
also  of  technical  importance. 

It  is  supposed  that  these  salt  layers  are  the  remains  of 
a  dried-up  arm  of  a  sea,  which,  after  the  first  evaporation, 
repeatedly  flowed  over  the  deposits  that  had  been  formed, 
and  in  this  way  produced  the  great  masses  of  salts  that 
are  found  in  the  district. 

Bromine  is  one  of  the  things  found  in  sea-water ;  this 
element  was  indeed  first  obtained  from  sea- water  in 


THE    NITROGEN   OF   PLANTS  47 

Southern  France.  Bromine  plays  an  important  part  in 
photography,  as  we  shall  see  later.  Now  the  Stassfurt  salts 
contain  bromine,  and  the  preparation  of  large  quantities 
of  this  substance  from  these  salts  forms  one  of  the  minor 
industries  carried  on  at  Stassfurt. 

We  must  now  return  to  the  consideration  of  the  nitrogen 
that  is  required  by  plants.  Plants  require  nitrogen  for 
the  building  up  of  what  is  called  vegetable  albumen — we 
shall  have  to  speak  of  this  substance  immediately  when 
dealing  with  true  albumen — a  substance  which  conditions  the 
life-functions  of  plants  in  a  similar  way  to  that  wherein 
animal  albumen  acts.  And  so  it  is  that  want  of  nitrogen 
is  synonymous  with  arrest  of  growth. 

We  did  not  find  any  nitrogen  in  the  ashes  of  plants 
(see  the  analyses  of  plant-ash  on  p.  37),  because  compounds 
of  nitrogen  are  not  fixed  in  the  fire,  but  are  volatilised  either 
unchanged  or  in  combination  with  other  elements ;  we 
considered  the  volatilisation  of  nitrogen  in  combination  with 
hydrogen,  as  ammonia  for  instance,  in  dealing  with  the 
manufacture  of  coal-gas. 

One  would  suppose  at  first  sight  that  plants  could  never 
lack  nitrogen  ;  we  know  that  the  leaves  of  plants  easily 
take  the  carbon  the  plants  require  from  the  air,  and  we 
also  know  that  10,000  parts  of  air  contain  only  3  parts  of 
carbonic  acid,  whereas  in  the  same  quantity  of  air  nearly  8,000 
parts  of  nitrogen  are  present  (see  p.  8).  But,  as  has  been 
often  said,  nitrogen  is  a  very  indifferent  gas,  and  most  plants 
possess  no  arrangement  for  directly  assimilating  this  inert 
material. 

It  is  true  that  the  air  contains  ammonia,  which  is  a 
nitrogen  compound  soluble  in  water ;  but  this  substance 
is  present  in  the  air  only  in  traces  which  must  be  reckoned 


48  CHEMISTRY  IN   DAILY  LIFE 

in  parts  per  million.  Now,  as  plants  are  not  able  to 
assimilate  nitrogen  compounds  by  their  leaves,  but  only 
by  their  roots,  it  follows  that,  at  most,  only  that  part  of 
this  ammonia  which  circulates  with  the  air  in  the  soil,  or 
that  which  percolates  into  the  soil  with  the  rain,  can  be 
available  for  the  plants;  and  this  quantity  is  quite  in- 
sufficient to  supply  the  nitrogen  required  by  the  plants. 

Investigations  made  since  1886  have  shown  that  certain 
bacilli  play  a  very  striking  part  in  the  process  whereby  plants 
assimilate  nitrogen.  There  are  certain  bacilli  in  tilled  soil 
which,  while  performing  their  vital  processes,  exhibit  the 
remarkable  property  of  causing  the  combination  of  nitrogen 
with  oxygen.  The  compounds  that  are  produced  in  this 
way  react,  in  turn,  with  substances  in  the  soil  to  form 
compounds  that  dissolve  in  water — chiefly  salts  of  nitric 
acid-  and  these  soluble  compounds  are  then  assimilated  by 
plants.  Nitric  acid  is  a  product  of  the  oxidation  of  nitrogen  ; 
it  is  a  compound  of  that  element  with  oxygen  and  hydrogen. 

Plants  are  known,  belonging  to  the  leguminous  class,  on 
whose  root-nodules  so  much  nitrogen-containing  material  is 
stored,  in  consequence  of  the  activity  of  bacilli,  that  the  soil 
is  constantly  rendered  richer  in  nitrogen  compounds  by  their 
growth  ;  such  plants  are  known  as  nitrogen-gatherers.  If, 
then,  plants  whose  roots  do  not  possess  this  property  are 
cultivated  on  a  certain  soil  which  has  been  sown  the  previous 
year  with  these  nitrogen-gatherers,  those  plants  find  a  store 
of  material  which  supports  their  growth,  although  the  soil  has 
not  been  directly  manured  with  nitrogen  compounds.  If  this 
method  of  manuring  is  adopted  the  money  value  of  the 
nitrogen  may  be  taken  as  about  40  marks  per  hectare  [about 
1 6  shillings  per  acre],  calculated  on  the  present  price  of  Chili 
saltpetre. 

Attempts  were    made   to   apply  these    nitrogen-gathering 


NITROGEN   COMPOUNDS  AS  MANURES  49 

bacilli  directly  to  soil-culture.  The  bacilli  were  bred  in  pure 
cultures  which  were  brought  into  the  market  with  the  name 
nitragin.  Before  they  were  sown,  the  seeds  were  soaked 
in  nitragin  diluted  with  thin  milk,  so  that  the  nitrogen- 
gathering  bacilli  adhered  to  each  seed.  The  results  of  many 
experiments,  made  from  the  year  1896,  have  led  to  such 
unsatisfactory  results  that  the  method  must  be  regarded  as 
valueless  to  agriculture. 

Now,  before  all  this  was  known,  experiments  had  shown 
that  the  addition  to  the  soil  of  materials  that  contain  nitrogen 
—or,  as  one  may  say,  the  assistance  of  the  activity  of  the 
bacilli — was  very  beneficial  to  the  growth  of  plants.  Those 
nitrogen  compounds  which  are  soluble  in  water  are  of  course 
the  most  efficient.  There  are  four  compounds  which  can  be 
obtained  in  such  quantities,  and  at  so  moderate  a  price,  as  to 
make  them  suitable  to  the  agriculturist  for  this  purpose. 

One  of  these  compounds  is  sulphate  of  ammonia ;  the 
second  is  Chili  saltpetre  ;  the  third  is  calcium  nitride  ;  and 
the  fourth  is  calcium  nitrate.  Until  1909,  ammonia  was 
obtained  only  from  the  gas-works.  In  its  chemical  relations 
ammonia  is  an  alkali  or  a  base,  for  these  names  have  to-day 
the  same  meaning.  The  characteristic  property  of  a  base  is 
that  it  is  able  to  combine  with  acids  ;  the  product  of  such 
combination  is  called  a  salt.  As  there  is  an  enormous 
number  of  acids  and  bases,  so  there  is  a  very  great  number 
of  salts  related  to  these  acids  and  bases. 

Bases  and  acids  may  be  gases,  liquids,  or  solids.  Am- 
monia, for  instance,  is  a  basic  gas,  aniline  is  a  liquid  base, 
carbonic  acid  is  an  acid  gas,  sulphuric  acid  is  a  liquid,  and 
silicic  acid  is  a  solid.  Silicic  acid  is  regarded  as  an  acid 
because  it  combines  with  bases  to  form  silicates  ;  for  instance, 
with  potash  it  forms  silicate  of  potash.  As  ammonia  gas  is 
4 


50  CHEMISTRY   IN   DAILY   LIFE 

very  soluble  in  water,  it  is  more  convenient  to  use  it  in  the 
form  of  an  aqueous  solution.  Inasmuch  as  ammonia  is 
commonly  sold  as  an  aqueous  solution,  it  is  often  supposed 
that  ammonia  is  a  liquid. 

Ammonia  is  used  in  agriculture  in  the  form  of  sulphate  of 
ammonia,  which  is  a  white  solid  formed  by  combining 
ammonia  with  sulphuric  acid ;  this  is  found  to  be  the  most 
suitable  compound  of  ammonia  to  use  as  a  manure  on 
the  fields. 

Nitre,  or  saltpetre,  is  the  second  source  of  nitrogen.  This 
substance  is  produced  by  combining  nitric  acid  with  potash 
or  soda ;  hence  one  speaks  of  potash  saltpetre  and  soda 
saltpetre.* 

Saltpetre  has  been  known  for  long,  and  has  been  used 
in  the  manufacture  of  gunpowder.  We  shall  have  to  consider 
gunpowder  and  the  more  recently  introduced  explosives  when 
we  have  finished  what  we  have  to  say  about  food-stuffs. 
Saltpetre  is,  however,  too  expensive  for  the  farmer.  The 
cheaper  soda  saltpetre  is  a  discovery  of  our  time.  This  salt 
is  generally  called  Chili  saltpetre,  from  the  name  of  the 
country  whence  it  comes.  There  are  great  stretches  of  land 
in  Chili  where  rain  never  falls,  and  where  therefore  the  soda 
saltpetre  that  is  formed  accumulates  in  the  soil.  The  manu- 
facture of  soda  saltpetre  began  about  1830  ;  the  process  con- 
sists in  lixiviating  with  water  the  soil  that  contains  the  salt, 
filtering,  concentrating  by  evaporation,  and  then  allowing  the 
salt  to  crystallise  out.  The  liquid  which  is  drained  off  from 

*  Salts  are  called,  ordinarily,  by  such  names  as  sulphate  of  potash, 
carbonate  of  soda,  etc.,  in  accordance  with  older  views  of  their  constitution. 
Chemists  now  regard  them  somewhat  differently,  and  speak  of  potassium 
sulpfate,  sodium  carbonate,  etc.  The  older  names  are  retained  in  this 
book,  as  it  is  quite  out  of  the  question  to  go  into  the  reason  for  the 
change. 


SALTPETRE  CALCIUM   NITRIDE  51 

the  crystals  is  called  the  mother-liquor ;  this  name  is  applied, 
in  a  general  way,  to  any  liquid  from  which  crystals  have 
separated. 

When  such  mother-liquors  are  evaporated,  the  salts  which 
were  contained  therein,  in  solution,  separate  out ;  salts 
obtained  in  this  way  are  called  mother-liquor  salts.  The 
mother-liquor  from  Chili  saltpetre  is  not  evaporated  com- 
pletely to  dryness,  because  it  is  possible  by  partially 
evaporating  this  liquor  to  obtain  the  small  quantities  of  the 
compounds  of  iodine  which  it  contains.  This  comparatively 
rare  element,  iodine,  is  at  present  obtained  chiefly  from  Chili. 
Experiments  have  shown  that  saltpetre  provides  plants  with 
nitrogen  more  quickly  and  more  thoroughly  than  any  other 
nitrogen-manure. 

The  third  source  of  nitrogen,  calcium  nitride,  came  into  use 
in  1903.  On  p.  35  we  learned  something  about  calcium 
carbide.  Professor  Franck  discovered  that  when  nitrogen  is 
passed  over  heated  calcium  carbide — and  nitrogen  can  be 
cheaply  obtained  from  the  air  (see  p.  9) — a  compound,  calcium 
nitride,  is  formed.  The  first  factory  of  calcium  nitride  was 
established,  in  1905,  by  a  Germany  company,  at  Piano  d'Orta 
in  Italy,  the  site  being  chosen  because  of  the  cheap  supply 
of  power  obtained  from  water.  The  yearly  output  of  this 
factory  is  80,000  centners  (nearly  4,000  tons).  A  consider- 
able amount  of  calcium  nitride  is  now  worked  up  into 
sulphate  of  ammonia,  in  the  factories,  and  in  this  way  the 
nitrogen  of  the  atmosphere  is  made  available  for  agriculture. 

The  problem  of  applying  atmospheric  nitrogen  to 
agriculture  was  solved  in  quite  a  different  way  by  Birke- 
land  and  Eyde.  It  had  been  known  for  long  that  traces 
of  nitric  acid  were  formed  by  passing  electric  sparks  through 
moist  air.  The  work  of  Birkeland  and  Eyde,  and  of  many 


CHEMISTRY   IN   DAILY   LIFE 


other  investigators  since  1909,  has  so  increased  the  yield  of 
nitric  acid  that  agriculturists  have  been  able  to  buy  nitric 
acid  produced  from  the  air,  in  the  form  of  nitrate  of  calcium, 
at  a  sufficiently  cheap  price. 

These  two  achievements  of  chemistry  have  caused  the 
agriculture  of  the  world  for  the  first  time  to  become  inde- 
pendent of  the  supply  of  Chili  saltpetre.  The  exhaustion  of 
the  deposits  in  Chili,  which  must  have  happened  after  about 
a  century  at  the  outside,  would  have  made  impossible  the 
carrying  on  of  agriculture  on  its  present  scale.  The  following 
table  presents  the  average  yield  of  wheat,  in  kilograms  per 
hectare,  in  different  countries,  calculated  on  the  average  of 
the  years  1905  to  1909.  This  table  shows  how  the  employ- 
ment of  artificial  nitrogenous  manures  increases  the  yield  in 
farming  industries.  [Kilogram  per  hectare  divided  by  125 
is  approximately  equal  to  hundredweights  per  acre.] 


Great  Britain 
Germany 
France 
Austria 
Canada 
Hungary 
Roumania    .. 
Italy 


Now  that  we  have  become  acquainted  with  the  methods 
whereby  plants  are  able  to  obtain  everything  they  require  for 
their  growth  from  the  inorganic  world,  including  therein  the 
air  which  surrounds  us,  let  us  pass  on  to  consider  the  food  of 
men  and  of  animals. 

Man  is  able  to  build  up  his  body  only  from  those  organic 
substances  which  have  already  been  put  together  by  plants. 
For  this  purpose  he  makes  use  of  fruit,  grain,  etc.  ;  but  he  can 
also  use  animals — oysters,  for  instance — or  parts  of  animals, 


Kilos. 

Kilos. 

2,100 

United  States  

920 

1,980 

Spain    

810 

1,380 

Argentine       

770 

,320 

Asiatic  Russia 

770 

,240 

British  Indies  

750 

,200 

Australia         

670 

,100 

European  Russia 

670 

,030 

DIGESTION   OF  FOOD  53 

such  as  their  flesh.  Animals  themselves  feed  on  plants  or 
on  other  animals,  so  that  the  nourishment  of  the  whole 
animal  kingdom  is  derived  primarily  from  the  vegetable 
kingdom. 

Everything  which  serves  us  as  a  food  finds  its  way  eventu- 
ally into  the  stomach.  Those  constituents  of  food  which  are 
to  be  used  for  building  up  the  body  go  into  solution  in  the 
stomach  and  the  intestines,  and  in  this  form  they  can  be 
taken  up  by  the  blood,  which  carries  to  each  part  of  the  body 
what  that  part  requires. 

Let  us  carry  out  processes  of  digestion  in  several  glass 
vessels  by  the  aid  of  gastric  juice.  The  coats  of  the  stomach 
secrete  a  substance  called  pepsin^  and  the  stomach,  in  its 
normal  state,  also  contains  a  small  quantity  averaging  about 
two-tenths  of  a  per  cent,  of  hydrochloric  acid.  These  two 
substances,  pepsin  and  hydrochloric  acid,  together  are  able  to 
make  soluble  the  undissolved  albumens  of  the  food  ;  or,  as  is 
generally  said,  to  transform  these  albumens  mto  peptones. 

When  a  stomach  is  soaked  in  glycerin,  the  pepsin  dissolves 
in  the  glycerin  ;  in  our  experiment  we  shall  employ  such  a 
solution  of  pepsin  in  glycerin.  The  experiment  is  made  in 
the  following  simple  manner. 

We  heat  a  chamber,  which  can  be  closed,  to  about  37°  C. 
[98*5°  F.],  which  is  approximately  the  temperature  of  the 
body,  and  we  place  four  glasses  containing  a  little  water 
in  the  warm  chamber.  In  one  of  these  glasses  we  place  some 
of  our  pepsin  solution,  into  another  we  pour  hydrochloric  acid, 
and  into  the  third  and  fourth  we  put  both  pepsin  and  hydro- 
chloric acid.  As  the  substance  to  be  digested  we  choose 
fibrin  (about  which  albuminoid  substance  we  shall  learn  more 
hereafter)  and  some  hard-boiled  white  of  eggs.  We  put  both 
of  these  substances  into  the  first  and  second  glasses,  and  only 


54 


CHEMISTRY   IN    DAILY   LIFE 


one  of  them  into  each  of  the  third  and   fourth  glasses  (see 
fig.  16). 

The  process  of  dissolving  albumen  is  not  a  chemical  re- 
action in  the  ordinary  meaning  of  that  term,  and  it  does  not 
take  place  instantaneously,  as  so  many  chemical  reactions  do. 
As  about  half  an  hour  must  elapse  before  a  noticeable 

quantity  of  the  al- 
bumen has  dissolved, 
we  shall  allow  the 
experiment  to  pro- 
ceed, and  come  back 
to  it  again  at  the  end 
of  the  lecture,  when 
we  shall  be  able  to 
convince  ourselves 
that  the  desired  result 
has  been  obtained. 

The  active  sub- 
stance in  the  stomach, 
which,  as  we  know,  is 
called  pepsin,  is  only 
active  in  the  presence 
of  acids ;  but  the 
substance  called  tryp- 
j/«,  which  causes 
digestion  in  the  intes- 
tines, is  effective  only  in  the  presence  of  alkali ;  the  contents 
of  the  intestines,  therefore,  show  an  alkaline  reaction. 

It  is  easy  to  understand  that,  when  substances  are  got  into 
solution  in  these  ways,  such  substances  pass  into  the  blood, 
and  are  carried  through  the  whole  of  the  body.  But  there  are 
other  questions  which  press  for  answers,  but  which  no  one  has 
as  yet  succeeded  in  answering. 


Fig.  16. 


DIGESTION    OF   FOOD  55 

We  have  taken  for  granted,  as  self-evident,  that  processes 
of  digestion  go  on  in  the  stomach.  But  the  stomach  itself 
consists  of  flesh — namely,  of  albuminoid  substances ;  why, 
then,  does  not  the  stomach  digest  itself?  how  can  it  resist 
the  action  of  the  digesting  fluid  ?  We  digest  a  goose's 
stomach  with  readiness ;  and  if  you  ascribe  part  of  the 
digestibility  to  the  process  of  cooking,  you  must  remember 
that  such  an  animal  as  a  dog  is  able  to  digest  an  uncooked 
goose's  stomach  without  trouble. 

No  certain  answer  has  yet  been  found  to  the  question  we 
have  proposed.  We  know  that  the  secretion  of  the  stomach 
is  acid,  and  that  the  blood  shows  an  alkaline  reaction  ;  and 
we  may  suppose  that  the  acid  and  the  alkali  neutralise  one 
another  in  the  coats  of  the  stomach,  and  that  the  process  of 
digestion  is  thus  put  an  end  to.  But  we  cannot  decide  at 
present  whether  this  is  or  is  not  the  actual  reason  of  the 
durability  of  the  stomach. 

There  are  many  other  unexplained  problems  connected 
with  the  process  of  digestion.  Not  to  be  tedious,  let  us 
select  only  one  of  these.  Where  does  the  stomach  get  the 
intelligence  which  enables  it  to  select  from  the  food  all 
those  things  that  are  required  by  the  body  as  a  whole  ? 
We  may  very  well  suppose  that  the  stomach  looks  after 
itself,  and  takes  what  it  requires  for  its  own  sustenance 
from  the  food- stuffs  that  come  into  it.  But  how  does 
the  stomach  know  what  quantity  of  phosphate  of  lime 
the  bones  require  for  their  existence,  and  what  the  brain 
requires  ?  How  does  the  whole  digestive  apparatus  find  out 
how  much  nourishment  must  be  given  to  the  blood  to  keep 
up  the  increase  of  the  body  till  the  twenty-second  year,  and 
no  longer  ? 

But  we   are   coming    nearer  to   the  difficult   problems   of 


56  CHEMISTRY   IN   DAILY    LIFE 

physiological  chemistry,  and  that  is  a  domain   into  which  we 
cannot  enter  here. 

To  be  frank,  we  cannot  say  exactly  what  hunger  or  thirst 
is.  One  man  feels  hunger  more  in  his  throat,  another  more 
in  his  stomach.  Nature  has,  however,  taken  care  that 
when  hunger  assails  us  we  should  know  that  this  dis- 
agreeable sensation  can  be  removed  by  taking  food  ;  and  as 
regards  the  choice  of  food  she  has  left  us  plenty  of  room 
for  selection. 

Looked  at  chemically,  food  materials  may  be  divided  into 
three  main  classes  :  the  albuminoids  (in  addition  to  gelatin)  ; 
the  fats  ;  and  the  carbohydrates  (starch  and  sugar). 

The  albuminoids  are  substances  which  contain  nitrogen  ; 
their  composition  is  very  complicated.  They  are  formed, 
naturally,  in  plants  (see  p.  59),  whence  they  find  their  way, 
with  other  food-stuffs,  into  the  animal  body.  Other,  very 
complicated,  albuminoid  substances  are  built  up  from  these 
in  the  animal  body ;  and  having  performed  their  proper 
functions,  they  finally  leave  the  body,  in  the  urine,  in  the 
form  of  a  substance  called  urea,  which  is  extremely  rich  in 
nitrogen  and  has  a  comparatively  simple  composition.  It  is 
easy  to  calculate  the  quantity  of  albuminoids  which  a  man  has 
used,  for  his  existence,  in  24  hours,  by  determining  the 
amount  of  nitrogen  in  the  urine  passed  in  that  time. 

The  name  albuminoids  is  derived  from  egg-albumen  ;  but 
in  the  course  of  time  it  has  received  a  very  wide  connotation, 
which  we  have  already  more  accurately  defined,  and  has 
come  to  be  applied  both  to  albumen-like  bodies  which  are 
soluble,  and  to  similar  bodies  which  are  insoluble,  in  water. 
The  albuminoids  which  are  soluble  in  water — the  albumen  of 
eggs,  for  instance — are  coagulated  by  boiling.  This  change 
is  a  very  remarkable  one.  At  any  rate,  there  is  not  another 


CURDLING  OF  MILK  57 

of  the  many  substances  that  have  been  made  artificially  by 
chemists  in  the  course  of  time  which  exhibits  this  property. 

The  most  important  albuminoid  of  milk,  which  is  called 
casein,  is  not  coagulated  by  boiling  ;  but  if  the  slightest  trace 
of  acid  be  present  in  the  milk  the  casein  separates  out  in 
flakes.  This  separation  is  made  visible  to  you  when  I  add 
a  few  drops  of  vinegar  to  some  milk.  Milk  goes  sour, 
apparently  spontaneously,  in  warm,  summer  weather,  and 
curdles  whether  you  will  or  not.  The  reason  of  this  souring 
is  as  follows.  Besides  containing  about  3  per  cent,  of 
casein,  milk  also  contains  more  than  4  per  cent,  of  a  sugar 
called  milk-sugar ;  this  sugar,  like  most  other  sugars,  can 
ferment — that  is  to  say,  it  can  be  transformed  under  definite 
conditions  into  other  substances — without  a  specific  chemical 
action. 

The  following  table  shows  the  average  composition  of  milk 
and  of  cream  : 

Milk.  Cream. 

Water      8770     68-82 

Casein      2*91  ) 

Albumen  soluble  in  water        0*52  )" 

Fat           3*32     22*66 

Milk-sugar          4*84     4*23 

Ash          0*71     0*53 

No  fermentation  can  occur  without  the  presence  of  certain 
organisms — fungi,  or  bacilli,  as  they  are  called  to-day  ;  these 
are  everywhere  in  the  air,  but  they  are  active  only  under 
certain  suitable  conditions.  The  lactic  acid  bacillus,  which  is 
so  called  because  it  changes  milk-sugar  into  lactic  acid — we 
shall  meet  with  this  organism  more  than  once  in  the  course 
of  these  lectures — begins  to  act  on  milk  at  a  temperature 
between  20°  and  30°  [68°  and  86°  R] ;  milk  therefore 
curdles,  by  the  formation  in  it  of  lactic  acid,  only  on 
warm  days. 


58  CHEMISTRY   IN    DAILY   LIFE 

When  milk  curdles  by  souring,  casein  separates  from  it. 
Milk  can  also  be  curdled  intentionally  by  means  of  rennet ; 
and  the  substance  which  separates  is  used  as  a  food-stuff, 
after  being  properly  manipulated,  and  is  called  cheese. 
Rennet  is  a  ferment  analogous  to  pepsin  ;  this  ferment  is  not, 
however,  present  in  all  stomachs,  but  it  is  found  especially  in 
the  mucous  membrane  of  the  fourth  stomach  of  the  calf. 
Because  of  the  importance  of  milk  as  a  nourishing  food 
for  children,  many  attempts  have  been  made  to  preserve  this 
liquid  for  a  lengthened  period — in  other  words,  to  prevent  it 
from  going  sour.  Soxhlet's  apparatus  is  now  used  in  many 
families  for  this  purpose.  In  this  process,  milk  is  heated  for 
some  time  in  a  closed  flask  to  100°  C.  [212°  F.] ;  all  the  bacilli 
in  the  milk  are  thus  killed,  and  also  all  other  bacteria  which 
might  bring  about  putrefaction.  As  long  as  the  vessel  is 
kept  firmly  closed,  bacilli  cannot  fall  into  the  milk  from  the 
air,  and  hence  souring,  curdling,  and  putrefaction  cannot 
occur. 

However,  milk  which  has  been  boiled  in  this  apparatus  is 
not  quite  the  same  as  unboiled  milk.  The  casein,  the  fat,  the 
milk-sugar,  etc.,  are  unchanged  ;  but  that  portion  of  the 
albuminoids,  other  than  casein,  which  is  soluble  in  water — 
and  which  amounts  (see  table,  p.  57)  to  about  one-sixth  of  the 
total  albuminoids — is  coagulated  by  the  continued  boiling, 
and  is  thus  made  more  difficult  to  digest.  It  is  customary 
nowadays  to  employ  a  more  convenient  form  of  apparatus  for 
boiling  milk,  which,  although  it  does  not  insure  the  absolute 
security  of  Soxhlet's  method,  is  found  to  be  more  suitable  for 
preparing  milk  for  children's  use,  provided  it  is  used  with 
reasonable  care. 

Besides  those  albuminoids  which  coagulate,  some  by  heat 
and  some  by  addition  of  acids,  there  are  other  substances 


FIBRIN    AND   BLOOD-SERUM  59 

of  this  class  which  remain  dissolved  as  long  as  they  are  in  a 
living  body,  but  solidify  very  soon  after  they  are  withdrawn 
therefrom.  Substances  of  this  kind  exist  in  blood  ;  and  when 
blood  is  exposed  to  the  air  it  soon  separates  into  a  solid  and  a 
liquid  portion.  The  solid,  red  mass  becomes  colourless  when 
it  is  washed  with  water,  and  the  washed  substance  is  called 
fibrin.  It  was  fibrin  that  we  employed  in  our  experiments  on 
digestion,  because  this  substance  has  been  found  to  be  readily 
peptonised  when  digested  artificially,  and  hence  it  is  very 
suitable  for  such  a  lecture  experiment. 

The  liquid  which  remains  when  fibrin  is  separated  from 
blood  is  called  blood-serum.  Since  1894,  serum  from  the 
blood  of  animals  has  been  used  as  a  curative  agent  in  several 
diseases  that  are  caused  by  bacilli ;  for  instance,  in  diphtheria. 
When  diphtheria-bacilli  grow  in  a  suitable  liquid  they  produce 
a  virulent  poison  ;  by  filtering  off  the  bacilli,  a  liquid  is 
obtained,  the  quantity  of  poison  in  which  cannot  increase, 
because  the  poison-producing  bacilli  have  been  removed.  If 
a  moderate  amount  of  this  liquid  is  injected  under  the  skin  of 
an  animal,  the  poison  in  the  liquid  acts  on  the  animal,  which 
soon  sickens  ;  but  at  the  same  time  an  antidote  to  the  poison 
is  produced.  By  repeating  the  injections,  the  antidote 
accumulates  in  the  serum  of  the  animal,  and  such  serum  is 
used  as  a  curative  agent  in  cases  of  diphtheria. 

We  shall  not  go  deeper  into  the  very  difficult  subject  of  the 
classification  of  the  albuminoids.  It  should  be  noted  that, 
speaking  chemically,  flesh  belongs  to  the  albuminoids,  inas- 
much as  it  is  a  very  complex  aggregate  of  nitrogen-containing 
substances. 

One  thing  only  is  to  be  remarked.  Albuminoids  occur 
in  the  vegetable  kingdom  ;  wheat-meal  contains  about 
10  per  cent.,  grass  from  2  to  3  per  cent.,  and  hay  from 
10  to  12  per  cent,  of  albuminoids.  Dried  potatoes — dried 


60  CHEMISTRY   IN   DAILY   LIFE 

in    a    heating    apparatus — contain    about    6    per    cent,    of 
albuminoids. 

It  is  customary  nowadays  for  farmers  to  buy  artificial 
fodder  when  they  have  not  raised  a  sufficient  quantity  of 
natural  fodder  for  their  cattle  ;  on  account  of  their  great 
nourishing  power  such  artificial  fodders  are  known  as  feeding- 
stuffs.  Most  of  these  feeding-stuffs  consist  of  the  cakes  that 
remain  when  the  oil  is  pressed  out  of  certain  plant-seeds 
which  are  rich  in  that  substance  ;  [hence  the  name  oil-cake]. 
These  substances  are  remarkable  for  the  large  quantity  of 
albuminoids  they  contain  ;  this  may  amount  to  50  per  cent., 
as,  for  instance,  in  cakes  made  from  the  seeds  of  the  sun- 
flower. In  order  to  avoid  the  application  of  the  term 
albumen  to  a  constituent  of  plant-seeds,  which  may  seem 
somewhat  strange  to  ordinary  ears,  it  is  customary  to  speak 
of  these  substances  as  prote'ids>  a  nomenclature  which  was 
introduced  into  the  chemistry  of  the  albuminoids  in  the 
forties  of  last  century. 

Let  us  now  see  what  are  the  results  of  our  experiments  on 
digestion  (see  p.  54).  Looking  at  the  contents  of  the  first  and 
second  glasses,  we  see  that  neither  the  fibrin  nor  the  hard- 
boiled  egg-albumen  has  been  at  all  changed  by  digestion  with 
pepsin  only ;  that  the  fibrin  has  been  caused  to  swell  up,  but 
has  not  been  dissolved,  by  the  hydrochloric  acid  only ;  while 
the  acid  has  produced  no  change  in  the  hard-boiled  egg- 
albumen.  Now,  looking  at  the  contents  of  the  third  and 
fourth  glasses,  we  see  that  the  mixture  of  pepsin  and  hydro- 
chloric acid  has  so  acted  on  the  fibrin  that  that  substance  has 
gone  entirely  into  solution  ;  if  we  examine  this  solution  more 
narrowly  we  shall  find  that  the  fibrin  has  been  changed  into  a 
peptone,  which,  as  we  know,  is  a  soluble  albuminoid.  The 
hard-boiled  white  of  eggs,  if  not  dissolved  and  changed  into 


DIGESTION   OF   FOOD— GELATIN  6 1 

peptones,  has  certainly  been  much  acted  on  by  the  mixture  of 
pepsin  and  hydrochloric  acid.  This  substance  is  not  so  easily 
digested  as  fibrin  ;  had  we  allowed  the  experiment  to  con- 
tinue for  a  longer  time  we  should  have  got  the  whole  of  the 
egg-white  into  solution. 

In  actual  digestion  things  will  of  course  proceed  in  a  similar 
way.  Hard  white  of  eggs  is  rightly  regarded  as  not  easy  to 
digest  ;  but  although  the  process  of  digestion  occupies  more 
time  in  this  than  in  some  other  cases — than,  for  instance,  in 
the  digestion  of  flesh — hard-boiled  eggs  are  not  harmful  to  a 
healthy  stomach,  but  they  are  not  to  be  recommended  when 
one's  stomach  is  out  of  order. 

The  albuminoids  are  exceedingly  complicated  substances, 
chemically  considered  ;  the  process  of  digestion  converts  them 
into  peptones.  In  recent  years,  Fischer,  professor  in  Berlin, 
has  succeeded  in  preparing  peptone-like  bodies  in  the  labora- 
tory. This  work  is  the  most  remarkable  which  has  yet  been 
done  in  the  domain  of  scientific  chemistry ;  the  further 
development  of  the  labours  of  the  talented  investigator  is 
awaited  by  the  scientific  world  with  the  greatest  attention. 

Before  leaving  the  albuminoids  we  must  just  glance  at  the 
substance  called  gelatin.  The  cartilage,  the  bones,  and  all 
the  ligatures  of  the  animal  body  contain  substances  which 
dissolve  in  water  when  boiled  therewith  for  some  time  and 
form  a  liquid  which  gelatinises  as  it  cools.  Gelatin  is  obtained 
by  drying  such  gelatinised  solutions.  As  thus  prepared, 
gelatin  is  used  as  a  glue. 

Gelatin  contains  a  large  quantity  of  nitrogen.  The  follow- 
ing analyses  show  that  the  percentage  of  nitrogen  in  this 
substance  does  not  differ  much  from  that  in  the  more 
characteristic  albuminoids :  gelatin  may,  indeed,  to  some 
extent  be  substituted  for  albumen  in  foods,  in  some  of  which 


62  CHEMISTRY   IN    DAILY   LIFE 

— for  instance,  in  that  prepared  by  boiling  bones — it  is  con- 
tained along  with  albumen  ;  it  is  also  found  in  soups  and 
sauces. 


Carbon 

Hydrogen 

Nitrogen 

Sulphur 

Oxygen 


Egg- 

Plant  Albumen 

Albumen. 

from  Wheat. 

Gelatin. 

52'25 

54'3 

50-1 

6-90 

7'2 

7'5 

15-25 

I6'2 

I7'5 

i  '93 

ro 

— 

23-67 

21-3 

24-9 

ICO'OO  lOO'O  lOO'O 


LECTURE     IV 

Mixed  diet — Butter — Margarine — Starch — The  sugars — Ripening  of  fruits 
—The  diet  of  diabetic  patients — Fruit-sugar — Bonbons — Burnt  sugar 
as  a  colouring  material — Cane  sugar — Saccharin — The  absorption  of 
food — Common  salt — Iron — Importance  of  cooking — Soups — Bread 
making — Boiling  potatoes. 

THE  albumen  which  is  consumed  in  food  serves  to  replace 
that  which  is  used  in  carrying  on  the  vital  functions  of  the 
body.  But  other  kinds  of  nourishment  besides  albuminoid 
substances  are  required  to  supply  the  energy  which  the  body 
constantly  requires,  for  instance,  for  moving  itself  as  a  whole, 
or  for  moving  parts  of  itself — say  for  continuing  the  action  of 
the  heart — and  also  for  constantly  maintaining  the  temperature 
of  the  body,  by  the  burning  of  carbon  finally  to  carbonic  acid, 
at  that  degree  which  is  necessary  for  the  proper  performance 
of  the  bodily  functions. 

The  simple  replacement  of  the  carbonic  acid  which  is 
expired  in  the  breath  (see  p.  10),  for  instance,  does  not 
require  the  presence  of  any  nitrogenous  food,  as  carbonic  acid 
is  composed  of  carbon  and  oxygen  only. 

Now  we  know  that  nature  has  given  us  a  fairly  wide  choice 
in  the  matter  of  food-materials,  and  the  quantity  of  carbon  in 
a  diet  very  rich  in  nitrogen  may  suffice  for  all  the  needs  of 
the  animal  body.  This  is  proved  by  the  case  of  beasts  of 
prey,  some  of  whom  consume  only  flesh,  which  has  been 

63 


64  CHEMISTRY   IN    DAILY   LIFE 

shown,  by  experiment,  to  contain  extremely  little  non- 
nitrogenous  food-materials,  to  be,  indeed,  an  almost  purely 
albuminoid  food. 

A  pure  albuminoid  diet  is  certainly  not  required  for  the 
proper  maintenance  of  the  body  ;  we  much  prefer  a  mixed 
diet — that  is  to  say,  we  take  various  dishes  in  the  course  of  a 
day,  which  dishes  contain  sufficient  albumen  to  make  up  for 
what  is  used  in  the  body,  and  also  sufficient  non-nitrogenous 
nourishment  to  carry  on  the  work  of  the  body  and  to  maintain 
the  bodily  temperature ;  and  we  supply  our  want  of  liquids 
by  adding  water  or  some  liquid  form  of  nourishment. 

The  non-nitrogenous  food-stuffs  belong  to  two  chief  classes 
—the  fats  and  the  carbohydrates.  As  the  fats  and  the  carbo- 
hydrates do  not  contain  nitrogen,  these  substances  take  their 
place  among  the  food -stuffs  by  virtue  of  the  carbon  which 
they  contain.  Fats  are  formed  chiefly  in  animals,  but  to 
some  extent  also  in  plants ;  plant-fats  are  generally  called 
oils  by  those  who  are  not  chemists.  On  the  other  hand,  all 
the  carbohydrates  which  are  used  as  foods  come  from  the 
vegetable  kingdom. 

The  fact,  so  often  noted  with  astonishment  by  travellers, 
that  the  Greenlanders  consume  large  quantities  of  blubber  and 
fat,  will  readily  be  understood  from  what  has  been  said.  As 
these  people  cannot  till  the  fields,  and  therefore  can  have 
neither  meal  nor  sugar,  etc.,  for  consumption,  they  are  obliged 
to  supply  all  their  needs  in  the  way  of  non -nitrogenous  food 
by  consuming  the  one  kind  of  such  food— fat— which  they  can 
get.  We  enjoy  both  kinds  of  non-nitrogenous  foods.  We 
consume  fats  in  the  form  of  fat  or  butter,  and  carbohydrates 
in  the  form  of  bread  (or  other  preparation  of  flour),  potatoes, 
and  the  like.  In  more  southern  latitudes  plant-fats,  such  as 


BUTTER — MARGARINE  65 

olive  oil,  are  used  as  foods.     Man  has  known  instinctively 
how  to  obtain  fats  and  carbohydrates  from  his  surroundings. 

A  very  large  part  of  the  fat?  consumed  in  our  latitudes  is 
consumed  in  the  form  of  butter,  which  is  made  from  milk. 
When  milk  is  allowed  to  stand  it  gradually  separates  into  two 
layers,  the  lighter  fat-globules  floating  upwards  and  forming 
the  cream,  and  the  milk,  deprived  of  fats — or  the  skim  milk- 
remaining  below.  When  the  cream  is  violently  agitated,  as  is 
done  in  churning,  the  single  fat-globules  gather  together  and 
become  solid,  and  so  form  butter. 

The  somewhat  high  price  of  butter  led  to  attempts  to 
fabricate  an  artificial  substitute.  These  attempts  were  success- 
ful in  France  about  the  year  1870.  This  substitute  for  butter 
was  made  until  a  few  years  ago  from  ox-tallow.  The  tallow 
is  melted  ;  the  liquid  is  completely  separated  from  pieces  of 
skin  by  filtration  ;  the  clear  liquid  is  mixed  with  a  little  salt, 
and  is  allowed  to  stand  for  twenty-four  hours  at  the  tempera- 
ture of  25°  C.  [77°  F.]  whereby  it  is  partially  solidified,  after 
which  it  is  pressed  in  an  apparatus  kept  at  25°  C.  The 
residue  in  the  presses,  which  consists  chiefly  of  stearate  of 
glycerin,  is  used  for  making  stearin  candles  (see  p.  19),  while 
that  which  flows  from  the  presses  comes  into  the  market  under 
the  name  of  oleomargarine.  If  oleomargarine  is  to  be  made 
into  artificial  butter  there  is  added  about  a  third  of  its  weight 
of  cotton-seed  oil  and  earth-nut  oil,  and  it  is  then  mixed  with 
about  half  its  weight  of  cows'  milk,  and  about  the  same 
quantity  of  water  is  added.  By  vigorous  beating  this  mixture 
is  caused  to  separate  gradually  into  two  parts,  one  of  which  is 
the  artificial  butter,  and  the  other  is  an  aqueous  liquid. 
Sweet  milk  is  used  for  the  better  sorts,  and  skim  milk  for  the 
cheaper  kinds,  of  artificial  butter. 

The  fat  which  is  left  in  fresh  animal  flesh  by  the  butcher  is 
5 


66  CHEMISTRY  IN   DAILY  LIFE 

most  generally  used  for  making  artificial  butter  ;  and  after 
that,  preference  is  given  to  the  fat  of  pigs,  large  quantities  of 
which  are  sent  into  the  market  from  North  America. 

Let  us  now  consider  the  carbohydrates. 

The  name  carbohydrates  is  derived  from  the  proportion  in 
which  the  elementary  constituents  of  these  substances  are 
contained  in  them.  This  class  of  bodies  includes  starch 
powders,  the  sugars,  and  other  similar  substances  with  which 
we  shall  become  acquainted  in  another  lecture.  The  sugar 
which  is  found  in  grapes,  and  which  is  generally  known  as 
grape  sugar,  has  the  following  composition,  stated  in  atoms  : 

GRAPE  SUGAR. 

6  atoms  of  carbon       (represented  by  the  letter  C). 

12        „        hydrogen  (          „  „  „     H). 

6        „        oxygen      (         „  „  „     O). 

Using  the  contractions  already  explained  (see  p.  23),  this 
composition  is  expressed  by  the  formula 

C6H1208. 

The  proportion  of  the  atoms  of  hydrogen  to  the  atoms  of 
oxygen  is  as  2  is  to  I,  which  is  the  same  as  the  proportion  of 
the  atoms  of  these  elements  in  water  whose  formula  is  H2O. 

It  used  to  be  supposed  that  these  substances  were  composed 
of  carbon  united  with  water ;  hence  the  name  carbohydrate 
was  given  to  all  of  them,  for  in  all  the  proportion  of  the 
hydrogen  atoms  to  the  atoms  of  oxygen  is  as  2  is  to  I. 

Very  remarkable  researches,  which  were  brought  towards 
completion  only  in  the  last  years  of  the  nineteenth  century, 
have  shown  that  the  conclusion  drawn  from  the  analytical 
results — namely,  that  those  substances  are  compounds  of 
carbon  and  water — is  not  justifiable.  The  name  carbohydrate 
is  therefore  quite  inapplicable ;  nevertheless,  it  is  retained  as 
a  convenient  general  designation  for  this  class  of  compounds. 


STARCH  67 

Starch,  which  is  a  most  important  carbohydrate,  is  found 
everywhere  in  the  vegetable  kingdom.  The  chlorophyll- 
containing  granules  of  leaves  are  able  to  make  use  of  the 
carbonic  acid  of  the  air  for  building  up  starch  (see  p.  36). 
Starch,  therefore,  is  found  in  all  the  green  parts  of  leaves. 
This  substance,  starch,  at  last  accumulates  in  those  organs  of 
plants  which  serve  as  storers  of  reserve  material  (see  p.  99). 
We  find  these  especially  in  the  bulbs  and  roots,  in  the  fruit, 
and  in  the  seeds. 

Whatever  be  the  source  of  the  starch,  the  composition  of  it 
is  always  expressed  by  the  chemical  formula  C6H10O5 ;  but 
the  granules  of  starch  obtained  from  different  plants  show 
noticeable  differences  when  looked  at  under  the  microscope. 

Starch  is  generally  prepared  from  potatoes,  wheat,  rice,  or 
maize.  The  process  consists,  in  the  main,  in  rasping  the 
potatoes,  etc.,  along  with  water,  and  passing  the  product 
through  fine  sieves  ;  the  coarser  parts  remain  on  the  sieves, 
while  the  starch  granules  pass  through  the  meshes  in 
suspension  in  water. 

The  turbid  liquid  that  is  obtained  in  this  way  is  allowed  to 
settle  in  barrels,  and  the  starch  gradually  falls  to  the  bottom. 
The  liquid  is  drawn  off,  the  deposited  starch  is  drained, 
and  finally  dried  at  a  temperature  which  must  not  be  too 
high,  as  if  moist  starch  is  heated  to  about  50°  or  60°  C. 
[120°  to  140°  F.]  it  is  completely  changed,  its  structure 
disappears,  and  it  becomes  what  we  call  paste. 

Starch  is  spoken  of  as  potato-starch,  wheat-starch,  etc., 
according  to  the  name  of  the  plant  from  which  it  has  been 
obtained.  Starches  which  come  from  foreign  countries  are 
generally  called  by  special  names,  such  as  arrowroot,  which  is 
obtained  from  the  roots  of  various  tropical  plants,  and  different 
specimens  of  which  are  not  identical. 

Sago-starch  is  somewhat  different  from  these  other  starches. 


68 


CHEMISTRY   IN    DAILY   LIFE 


It  is  obtained  from  the  pith  of  certain  palms  by  grinding  in 
the  same  way  as  potato-starch  is  made.  After  being  com- 
pletely dried  the  substance  is  allowed  to  fall  through  sieves  on 
to  warm  metallic  plates.  This  causes  a  partial  conversion 
into  paste  of  the  exterior  parts  of  the  granules,  and  these 
gather  together  into  little  round  balls  that  are  sent  into  the 
market  under  the  name  of  sago. 

The  following  analyses  show  the  quantities  of  starch  and 
other  constituents  in  the  seeds  and  tubers  that  are  most 
commonly  consumed.  The  analyses  represent  the  composition 
of  ground  corn,  as  it  is  only  in  this  form  that  the  grains  of 
wheat,  rye,  etc.,  are  used  as  foods. 


Finest 

Rye-meal, 

Potatoes, 

Wheat- 

mean 

mean 

meal. 

composition. 

composition. 

Water    

...      14-86 

I5'o6 

75-48  per 

cent. 

Albuminoids     ... 

...        8-91 

II-52 

i  '95 

5) 

Fats       

...      ri6 

179 

0-15 

H 

1 

(Starch  

...    65'93 

62-00 

2069 

V 

[Sugar     

...      2-23 

0-95 

— 

M 

f 

\  Gum  and  Dextrin 

6*03 

4-86 

— 

K 

(.Cellulose 

•••      0-33 

2'II 

0-75 

M 

Ash         

...      0-55 

I-7I 

0-98 

„ 

lOO'OO 


lOO'OO 


100-00        „ 

Bran,  that  is  the  husks  of  the  grain  which  do  not  pass 
through  the  sieves  wherein  the  grain  is  shaken  after  grinding, 
is  used  as  fodder  for  cattle.  Analyses  of  bran  give  the 
following  results  : 

Water 

Albu; 

Fats 

Cart 

Celli 

Ash 


Wheat-bran. 

Rye-bran. 

minoids          ...         ...         ...         14*1 

14*5        „ 

•ohydrates      56^0 
alose     ...         ...         ...         .  .           7'2 

4        » 
59'o        „ 

fi'o 

r-g 

}» 

A'  A 

4  °         » 

100*0 


lOO'O 


THE  SUGARS  69 

Bran  is  richer  in  albuminoids  than  flour  ;  hence,  bread  made 
with  the  husks  as  well  as  the  grain  of  wheat  and  rye  is  very 
nourishing.  The  appearance  and  taste  of  such  bread  are  often 
objected  to. 

These  analyses  show  a  certain  amount  of  cellulose  in  wheat, 
rye-meal,  potatoes,  and  bran  ;  this  substance  is  a  carbohydrate, 
and  its  composition  is  expressed  by  the  formula  C6H10O5 ;  but 
as  it  is  quite  indigestible,  it  does  not  represent  any  nutritive 
element. 

We  must  now  proceed  to  the  consideration  of  the  sugars. 
Although  a  great  many  kinds  of  sugar  are  found  in  nature, 
yet  the  varieties  of  sugar  are  much  less  numerous  than  the 
different  kinds  of  starch.  Starches  and  sugars  are  nearly 
related  to  one  another,  and  starches  are  converted  into 
sugars,  especially  into  grape  sugars,  with  the  greatest  ease. 

We  may  often  notice  this  change  taking  place  in  ordinary 
life.  Unripe  fruits  have  not  a  sweet  taste  ;  but  some  of  them 
—for  instance,  strawberries — acquire  this  taste  in  a  few  hours. 
The  cause  of  this  process  is  to  be  found  in  the  change  of 
a  portion  of  the  starch  contained  in  the  strawberries  into 
sugar.  This  change  occurs  not  only  when  the  fruit  ripens, 
but  it  may  also  be  brought  about  by  cooling  the  fruit  below 
o°  C.  [32°  F.].  For  instance,  we  know  that  the  taste  of 
potatoes  which  have  been  frozen  is  sweet,  although  not 
altogether  agreeable.  The  cause  is  the  same  in  both  cases. 

The  rapid  conversion  of  starch  into  sugar  may  be  demon- 
strated by  adding  powdered  starch  to  some  water  that 
contains  a  little  acid,  say  hydrochloric  acid,  and  boiling  for  a 
short  time  ;  a  portion  of  the  starch  is  thus  converted  into 
sugar,  and  the  presence  of  sugar  may  be  shown  by  making 
use  of  the  following  chemical  reaction.  If  we  add  caustic 


70  CHEMISTRY   IN    DAILY   LIFE 

soda  and  copper  sulphate  (blue  vitriol)  to  some  water  we  get 
a  bluish  precipitate  of  copper  hydroxide  ;  and  if  we  now  boil 
for  a  little  time,  this  bluish  precipitate  is  changed  into  black 
oxide  of  copper.  The  presence  of  starch  does  not  alter  this 
reaction  ;  but  if  we  boil  some  starch  with  a  little  hydrochloric 
acid,  and  then  add  caustic  soda  and  a  solution  of  copper 
sulphate  to  this  liquid,  we  do  not  obtain  a  blue  precipitate, 
but  a  sky-blue  liquid  ;  if  we  now  boil  this  blue  liquid  there 
is  formed  in  it,  not  a  black,  but  a  red,  precipitate  of  cuprous 
oxide  (protoxide  of  copper).  This  reaction  is  characteristic 
of  grape  sugar.* 

The  sugar  that  is  produced  in  this  way  from  starch  is 
grape  sugar.  The  chemical  process  is  easily  understood. 
That  starch  may  be  changed  into  sugar  it  is  only  necessary 
for  the  starch  to  combine  with  the  elements  of  water. 
Thus, 

Starch,  takes  up  water,  and  produces  grape  sugar, 

which  consists  of  which  consists  of  which  consists  of 

6  atoms  of  carbon  6  atoms  of  carbon 

10  atoms  of  hydrogen     2  atoms  of  hydrogen      12  atoms  of  hydrogen 

5  atoms  of  oxygen          i  atom  of  oxygen  6  atoms  of  oxygen 

The  change  may  be  represented  more  shortly  in  this 
way  : 

C6H1005  +  H20  =  CttH1206. 

Starch.        Water.     Grape-sugar. 

*  When  this  reaction  is  applied  to  urine  it  enables  the  practitioner  to 
diagnose  diabetes,  as  diabetic  patients  excrete  grape  sugar. 

From  what  we  now  know  it  is  easy  to  understand  the  reason  for  the 
special  diet  which  is  prescribed  to  such  patients.  Except  in  the  most 
advanced  stages  of  diabetes,  when  all  the  material  transformations  that 
normally  occur  in  the  body  are  thrown  into  complete  disorder  (and  such 
changes  we  shall  not  of  course  consider  here),  albumen  cannot  be 
changed  into  sugar ;  there  is  also  no  intimate  chemical  connection 
between  fats  and  sugar  ;  but  we  have  just  convinced  ourselves  that 
starch  and  sugar  are  very  closely  related.  If,  then,  a  diabetic  patient  is 


GLUCOSE  71 

There  are  certain  substances  which  stand  between  starch 
and  grape  sugar  ;  the  best  known  of  these  is  dextrin,  which 
can  be  prepared,  among  other  ways,  by  heating  starch  to 
170° — 200°  C.  [340°— 390°  F.].  Dextrin  is  much  used  as  a 
substitute  for  gum  arabic. 

Grape  sugar  is  manufactured  by  boiling  starch  with  acids, 
and  is  sent  into  the  market  under  the  name  of  starch-sugar,  or 
more  generally,  glucose.  As  it  is  very  difficult  to  cause  this 
sugar  to  crystallise,  even  when  working  in  the  laboratory 
on  a  small  scale,  commercial  glucose  presents  the  form  of  a 
syrup.  This  syrup  forms  a  passable  substitute  for  honey.  It 
is  much  used  for  the  preparation  of  gingerbread  biscuits  ;  but 
its  chief  application  is  in  the  making  of  bonbons^  as  when 
these  are  made  by  using  glucose  they  are  not  so  hard  as  if 
cane  sugar  were  employed. 

Glucose  is  also  employed  for  making  sugar-colouring. 
If  one  heats  a  little  glucose  in  a  glass  vessel  till  it  becomes 
dark  brown,  allows  it  to  cool,  and  then  adds  some  water, 
the  colour  changes  to  the  yellowish  brown  tint  of  cognac  ; 
on  further  standing  the  colour  deepens  and  becomes  that  of 
dark  coloured  beer,  although,  as  we  shall  learn  hereafter,  the 
colour  of  such  beer  is  not  produced  in  this  way. 

As  this  sugar-colouring  is  quite  harmless,  it  is  very  useful 
for  colouring  articles  of  food  or  confectionery. 

put  on  a  diet  of  albuminoids  and  fats — if  he  consume  flesh,  eggs,  butter, 
and  the  like — he  will  not  excrete  any  sugar.  But  if  he  is  allowed  to 
consume  dishes  prepared  from  meals  or  potatoes,  or  such  vegetable 
products,  all  of  which  contain  much  starch,  these  will  give  rise  to  the 
excretion  of  greater  or  smaller  quantities  of  sugar  ;  he  should  therefore 
be  bidden  to  abstain  from  such  foods  as  far  as  he  possibly  can. 

In  the  less  serious  stages  of  the  disease  the  use  of  certain  quantities  of 
starchy  foods  may  be  valuable  for  the  general  nourishment  of  the  body 
of  the  patient,  and  for  this  reason  he  may  be  allowed  to  consume  a  little, 
but  only  a  little,  wheaten  or  rye  bread,  etc, 


72  CHEMISTRY   IN    DAILY   LIFE 

Cane  sugar,  which  is  used  by  us  every  day  and  comes  as  a 
sweetening  into  every  meal,  is  of  more  interest  to  us  than 
glucose,  which  we  only  occasionally  see  as  such  in  our 
ordinary  way  of  living.  Before  the  introduction  of  cane 
sugar  honey  was  the  only  sweetening  material  ;  and  it  is 
very  doubtful  whether  we  should  now  be  pleased  with  the 
sweetened  dishes,  tasting  of  honey,  which  the  ancient  Romans 
set  before  their  guests  at  their  feasts,  or  with  those  honeyed 
preparations  that  were  consumed  in  the  earlier  Middle  Ages 
in  the  patrician  houses  of  Nurnberg. 

As  its  name  implies,  cane  sugar  is  the  produce  of  a  cane- 
like  plant  ;  it  is  got  from  the  sugar-cane.  This  plant  grows 
only  in  Southern  climates  ;  the  knowledge  of  it  was  brought 
to  Europe  by  the  Crusaders.  At  first  the  sweet  juice  of 
the  plant  was  used  in  the  form  of  a  syrup  ;  the  preparation 
of  the  solid  sugar  dates  from  the  year  1400.  About  one 
hundred  years  later  began  the  process  of  refining  cane  sugar, 
by  dissolving  the  crude  sugar  in  water,  clearing  the  solution, 
and  allowing  the  much  purer  sugar  to  crystallise  out,  after 
boiling. 

As  soon  as  cane  sugar  had  become  an  easily  transported 
article  of  commerce  the  manufacture  of  it  advanced  rapidly, 
and  the  sugar-cane  began  to  be  cultivated  in  every  country 
where  the  climate  allowed  of  its  growth.  The  plant  was 
introduced  into  Central  America,  especially  into  the  West 
Indies,  about  1500 ;  and  after  about  six  years  so  much  sugar 
was  manufactured  there,  by  the  labour  of  slaves  shipped  from 
Africa,  that  the  cultivation  of  the  cane  almost  ceased  in  other 
parts  of  the  world,  even  in  the  East  Indies  where  the  climate 
was  well  suited  for  this  purpose.  The  plant  was  introduced 
at  an  early  date  into  Sicily  by  the  victorious  Arabians  ;  and 
that  island  is  the  most  northern  country  where  the  cultivation 
has  been  attempted.  But  the  industry  has  disappeared  from 


BEETROOT  SUGAR  73 

Sicily,  and  from  Europe  in  general,  since  the  American  over- 
production began. 

In  1747  the  Berlin  chemist  Marggraf  discovered  that  the 
same  sugar  which  is  obtained  from  the  sugar-cane  exists 
in  beetroots.  This  discovery  was  of  the  greatest  importance 
to  European  agriculture,  as  it  introduced  a  new,  and  for  a 
long  time  very  profitable,  crop. 

Marggraf  was  perfectly  conscious  of  the  far-reaching 
character  of  his  discovery.  A  kinsman  of  his,  named  Achard, 
very  soon  endeavoured  to  manufacture  sugar  from  beetroots 
on  a  large  scale,  on  his  land  at  Kaulsdorf,  near  Berlin,  but 
without  success,  because  the  cheap  colonial  sugar  made  it 
impossible  to  run  a  paying  factory  in  Europe  at  that  time. 
But  the  state  of  affairs  was  altered  by  political  changes.  In 
consequence  of  the  Continental  blockade  of  the  first  Napoleon, 
the  price  of  all  colonial  productions  which  had  until  then 
been  imported  into  Europe  by  the  English  rose  immensely, 
and  this  was  especially  true  of  sugar,  the  price  of  which  rose 
to  four  shillings  per  pound.  Under  these  conditions  the 
manufacture  of  beetroot  sugar  was  bound  to  be  a  paying 
business,  and  this  business  was  eagerly  undertaken. 

The  raising  of  the  Continental  blockade  ruined  most  of 
the  sugar  factories  then  in  work ;  but  so  much  experience 
had  been  amassed  in  the  manufacture  that  at  last  this 
sugar  gained  a  firm  hold  on  the  market  in  opposition  to  the 
colonial  sugar,  especially  as  the  latter,  being  a  very  convenient 
object  of  taxation,  was  obliged  to  pay  a  high  import  duty. 

The  manufacture  of  sugar  from  beetroots  has  in  the  course 
of  years  become  an  enormous  concern,  and  it  has  been 
brought  to  great  perfection  by  the  combined  action  of 
science  and  industry.  The  following  figures  make  this  very 
evident. 


74  CHEMISTRY   IN   DAILY   LIFE 

To  obtain  100  Ibs.  of  sugar  there  were  required — 

In  the  year  1836 1, 800  Ibs.  of  beetroot. 

„          1842 1,600    „  „ 

1857 1,200    „ 

„          1871 1,100    „  , 

„          1900 75°    »  » 

Marggraf  found  that  the  beetroots  cultivated  in  his  time 
contained  rather  more  than  6  per  cent,  of  sugar.  The  per- 
centage has  been  raised  since  then  by  the  proper  choice 
of  roots  and  manures.  An  average  of  14  per  cent,  was 
obtained  in  1890,  and  about  18  per  cent,  in  1910. 

Until  the  year  1900  the  production  of  beet  sugar  increased 
much  more  rapidly  than  that  of  cane  sugar.  The  following 
table  gives  some  data  : — 


Production  in  tons  =  1000  kilograms. 

Percentage  of 
Beet  sujjar 

Year. 

Cane  Sugar. 

Beet  Sugar. 

Total. 

produced. 

1840 

1,100,000 

50,000 

1,150,000 

4'35 

1880 

1,852,000 

1,402,000 

3,254,000 

43-08 

1890 

2,069,000 

3,633,000 

5,702,000 

6370 

IQOO 

2,862,OCO 

5,575,000 

8,437,000 

65-08 

IQIO 

8,  1  70,000 

6,510,000 

14,680,000 

44'33 

The  manufacture  of  cane  sugar  has  increased  more  rapidly 
than  that  of  beet  sugar  since  1900.  In  Germany,  at  present, 
the  maximum  quantity  of  sugar  obtained  from  the  beets 
grown  on  one  hectare  of  land  is  5,000  kilograms  (in  1870 
it  was  2,000  kilograms)  ;  the  intelligent  Dutch  sugar  growers 
in  Java  obtain  as  much  as  15,000  kilograms  of  sugar  from 
the  sugar-cane  grown  on  a  hectare  of  land. 

In  order  to  extract  the  sugar  the  beetroots  are  first  of  all 
crushed  and  rasped  to  a  pulp,  and  all  the  sugar  is  then 
removed  by  treatment  for  several  hours  in  what  is  called 
a  battery  of  diffuscrs.  The  juice  must  then  be  evaporated, 


CRYSTALLISING  OF  SUGAR  75 

This  process  presents  many  difficulties,  because  if  sugar-syrup 
is  boiled  for  a  long  time  the  sugar  is  altered  and  becomes 
non-crystallisable.  But  the  difficulties  have  been  overcome 
by  carrying  on  the  evaporation  of  the  sugar  solution  under  a 
greatly  reduced  pressure,  instead  of  in  open  vessels  as  in 
ordinary  processes  of  boiling  down ;  the  syrup  boils  at  a 
much  lower  temperature  in  an  evacuated  vessel  than  it  would 
do  in  an  open  vessel.  In  the  first  lecture  we  had  ocular 
demonstration  of  the  pressure  of  the  air  (see  p.  3).  Suppose 
water  is  heated  ;  before  the  vapour  of  the  water  can  rise 
freely — that  is,  before  the  water  can  boil — the  pressure  of  this 
vapour  upwards  must  be  sufficient  to  overcome  the  down- 
ward pressure  of  the  atmosphere.  Now  if  the  air  is  removed 
from  a  closed  vessel — say  from  a  copper  vessel,  such  as  is 
used  in  the  sugar  factory — by  means  of  an  air-pump,  the 
vapour  of  water  in  such  a  vessel  will  ascend  much  more 
easily  than  if  the  water  were  in  an  open  vessel ;  and 
therefore  water  will  boil  in  such  a  vessel  at  a  temperature 
much  lower  than  its  ordinary  boiling-point,  which  is  100°  C. 
[212°  F.]. 

The  process  may  perhaps  be  more  easily  understood  by 
considering  the  following  fact.  Water  boils  on  the  top  of 
Mont  Blanc  at  85°  C.  [185°  F.],  because  the  height  of  the 
column  of  air  which  presses  on  the  surface  of  the  water  is 
as  much  less  than  that  of  the  air-column  at  the  level  of  the 
sea  as  is  the  height  of  the  top  of  the  mountain  above 
the  sea-level. 

The  sugar-juice  can  be  boiled  down  without  any  danger 
at  the  greatly  reduced  temperature  obtained  by  using  an 
apparatus  from  which  most  of  the  air  has  been  removed. 
After  sufficient  evaporation  and  cooling,  sugar  separates 
from  the  liquid  in  crystals,  which  are  then  purified  and  sent 
into  the  market  in  the  form  of  sugar-loaves,  Animal 


76  CHEMISTRY   IN    DAILY   LIFE 

charcoal  (see  p.  42)  is  made  use  of  for  effecting  the  complete 
decolourisation  of  the  syrup. 

The  mother-liquor  (see  p.  51)  from  crystallised  sugar  is 
known  as  molasses.  For  a  long  time  no  method  could  be 
found  for  obtaining  the  sugar  that  remained  in  this  liquid, 
but,  by  methods  suggested  by  chemists  about  the  year  1882, 
the  whole  of  the  sugar  can  now  be  withdrawn  from  molasses. 
Large  quantities  of  molasses  are  now  used  as  fodder  for 
cows  ;  the  molasses  are  mixed  with  finely  chopped  straw, 
preferably  with  straw  from  rape  plants. 

In  connection  with  the  sugars  it  will  be  well  to  say  a  word 
on  the  most  recently  introduced  sweetening  material,  called 
saccharin^  a  name  derived  from  saccharumy  the  Latin  word 
for  sugar. 

Of  the  vast  number  of  chemical  compounds  there  are 
certain  to  be  many  with  a  pronounced  taste  ;  the  acids,  for 
instance,  take  their  name  from  the  fact  that  the  earliest 
discovered  substances  of  this  class  had  an  acid  taste.  Bases 
such  as  potash  or  soda  have  a  caustic,  soap-like  taste.  Some 
salts,  that  is  compounds  of  acids  and  bases,  have  a  pure 
salt-like  taste,  others  a  bitter  taste,  and  some  are  tasteless. 
The  tastes  of  the  many  compounds  which  do  not  belong 
to  one  or  other  of  these  three  classes  are  almost  infinitely 
varied.  Omitting  sugar,  a  few  substances  with  a  somewhat 
sweetish  taste,  such  as  alanine^  have  been  known  for  long. 
But  it  happens  that  only  one  substance  has  been  discovered, 
up  till  now,  which  is  so  extraordinarily  sweet  that  one  part 
of  it  is  equal  in  sweetening  power  to  300  parts  of  sugar  :  this 
substance  is  saccharin.  The  chemical  composition  of  saccharin 
is  very  complex  ;  its  systematic  chemical  name  is  sulpho- 
benzimide. 

Saccharin  has  no  value  as  a  food,  quite  independently  of 


SACCHARIN — CHANGE  OF   DIET  77 

the  fact  that  it  is  never  consumed  except  in  very  minute 
quantities.  It  may  be  used  for  sweetening  all  sorts  of  things ; 
but  it  has  proved  beneficial  chiefly  to  patients  suffering  from 
diabetes,  who  are  able  by  its  help  to  enjoy  the  sweet  taste 
of  dishes  which  they  were  obliged  wholly  to  renounce  before 
the  discovery  of  saccharin. 

The  advantages  of  sweetening  dishes  in  this  way  should 
not  be  regarded  as  small,  inasmuch  as  many  foods  are  thus 
made  more  easy  of  consumption.  For  there  is  no  doubt 
that  emotional  conditions,  as  well  as  physical  needs,  play 
a  part  in  the  absorption  of  foods.  We  continue  to  take  only 
such  means  of  nourishment  as  have  been  made  agreeable  to 
our  palates  in  one  way  or  another.  It  appears  as  if  such 
condiments  as  salt,  pepper,  and  mustard  were  required  to 
rouse  the  digestive  processes  into  activity.  Indeed,  we  go 
further  than  this ;  we  regularly  enjoy  warm  decoctions  of 
coffee  or  tea,  the  nourishing  value  of  which  is  nil,  because 
we  know  by  experience  that  these  make  easier  the  con- 
sumption of  solid  nourishment. 

Spirituous  drinks  occupy  a  position  between  those  things 
we  consume  for  nourishment  and  those  we  consume  for 
pleasure  ;  and  when  we  go  more  into  detail  we  shall  find 
that  these  liquids  belong  more  to  the  latter  than  to  the 
former  class. 

Experience  teaches  us  that  men  fairly  easily  get  accustomed 
to  one  kind  of  delicacy  or  beverage,  so  that  the  continued 
use  of  the  same  thing  either  leads  to  satiety,  or  the  wished- 
for  effect  can  be  obtained  only  by  increasing  the  quantity, 
with  the  result  that  excess  is  indulged  in,  and  deplorable 
consequences  follow.  Hence  it  follows  that  there  must  be 
a  considerable  variety  of  dishes  in  a  diet  which  is  suitable 
for  constant  use,  and  that  a  careful  selection  must  be  made 


78  CHEMISTRY  IN   DAILY  LIFE 

of  the  condiments  which  are  added  to  give  flavour  and 
agreeableness  to  the  dishes.  Happily  experience  and  daily 
habit  have  taught  most  housewives  how  to  insure  this  result. 

Refinement  of  cooking  is  by  no  means  an  improper  object 
of  endeavour.  It  is  certainly  as  permissible  as  thousands  of 
those  other  attempts  after  enjoyment  which  seek  to  make 
life  more  pleasant.  By  this  we  do  not  mean  to  advocate 
the  consumption  of  dinners  with  an  interminable  array  of 
different  courses,  but  only  to  assert  that  the  housewife  does 
well  when  she  takes  care  that  what  is  put  on  the  table  is  so 
prepared  that  it  may  be  agreeable  and  may  be  consumed 
with  pleasure. 

It  should  not  be  overlooked  that  the  preparation  of  food- 
stuffs on  a  large  scale  brings  many  advantages  with  it.  In 
towns  every  one  has  his  bread  from  the  baker,  and  so  he 
gets  it  fresh  every  day  and  with  a  good  flavour  ;  but  in 
those  country  parts  where  each  household  must  do  its  own 
baking  the  bread  is  generally  stale,  because  it  is  impossible 
to  prepare  every  day  just  what  is  wanted  for  the  day's 
consumption.  No  one  would  assert  that  to  bring  about  an 
improvement  in  the  quality  of  bread  for  general  consumption 
would  be  either  wasteful  or  luxurious. 

The  preserved  vegetables,  which  make  it  possible  to  enjoy 
vegetable  diet  in  winter  almost  as  cheaply  as  in  summer,  and 
also  those  preparations  of  meat  and  fish  which  are  much 
used  nowadays,  belong  to  the  substances  we  are  now  con- 
sidering. Such  things  enable  one  to  vary  one's  meals  at 
a  very  small  cost. 

The  well-known  saying,  "  toujours  perdrix?  shows  very 
forcibly  that  a  thing  which  in  itself  is  extremely  good  eating, 
and  when  taken  occasionally  is  peculiarly  pleasurable  to  the 
palate,  becomes  altogether  unenjoyable  when  consumed 
constantly  for  a  long  time. 


MINERAL  CONSTITUENTS  OF   FOOD  79 

It  is  not  only  human  beings  who  object  to  monotony  in 
diet ;  flesh-eating  animals  do  the  same.  Rats  certainly  soon 
die  if  they  can  get  nothing  but  boiled  flesh ;  after  a  time  they 
refuse  to  touch  it,  and  prefer  to  starve  rather  than  to  eat 
the  flesh.  Birds  seem  to  differ  in  this  respect  from  flesh- 
eaters,  as  they  may  be  fed  in  captivity  for  years  on  the 
same  kind  of  grain  or  seed  without  taking  any  hurt. 

The  analyses  given  on  p.  68  of  corn-grains  certainly  show 
us  that  these  taken  alone  represent  a  mixed  diet,  and  this 
may  be  the  reason  why  they  can  be  used  as  food  for  a 
long  time. 

To  maintain  life  we  require  water  and  certain  inorganic 
salts,  besides  albuminoids,  fats,  and  carbohydrates.  The  only 
inorganic  salt  which  we  use  directly  in  our  food  is  common 
salt,  which  is  a  substance  that  we  add  intentionally  to  most 
dishes,  and  a  substance  which  seems  to  have  a  specific 
beneficial  effect  on  the  animal  body.  We  notice  that  where 
opportunity  serves  many  animals  resort  eagerly  and  regularly 
to  salt  deposits. 

The  analyses  of  food-stuffs  that  have  been  given — and  those 
which  are  to  follow — show  that  the  other  salts  which  we 
require,  such,  for  instance,  as  phosphate  of  lime  for  the  bones, 
are  contained  in  sufficient  quantities  in  our  ordinary  foods. 
The  total  quantity  of  these  salts  is  represented  as  ashes  in  the 
analyses.  Iron  is  the  only  one  of  these  inorganic  substances 
which  possesses  much  interest  when  a  general  survey  is  being 
made  of  the  subject. 

The  quantity  of  iron  required  daily  by  a  human  being  is 
extremely  small  ;  it  may  be  taken  as  one-seventh  of  a  milli- 
gram per  kilo,  of  body-weight  [about  y^Vrr  of  a  grain  per  lb.]. 
This  amounts  to  only  about  3  grams  per  year  for  a  person 
weighing  50  kilo,  [about  45  grains  for  a  person  of  8  stone 


8o 


CHEMISTRY   IN    DAILY   LIFE 


weight]  ;  nevertheless,  it  is  well  known  that  an  insufficient 
absorption  of  iron  leads  to  chlorosis  and  to  many  subsequent 
disorders.  When  one  is  in  health  the  requisite  quantity  of 
iron  is  quite  provided  for  by  the  food  consumed  ;  but  in 
certain  ailments,  such  as  chlorosis  in  young  girls,  the  power  of 
the  organism  to  assimilate  iron  from  the  food  is  so  reduced 
that  iron  must  be  supplied  artificially  if  the  requisite  absorption 
of  that  substance  is  to  take  place.  It  is  often  very  difficult 
to  find  the  proper  iron  tonic,  because  these  medicines  affect 
different  individuals  in  very  different  ways.  For  this  reason, 
new  preparations  of  iron  are  constantly  making  their  appear- 
ance. This  at  least  can  be  asserted  to-day,  that  the  power  of 
iron  compounds,  taken  as  medicines,  to  increase  the  formation 
of  blood  is  an  incontestable  fact  which  is  no  longer  disputed 
by  any  physician.  The  quantities  of  iron  and  of  chalk  in 
different  food-stuffs  are  given  in  the  following  table,  for  the 
especial  reason  that  these  numbers  deal  with  a  matter  which 
is  of  great  interest  to  many  people. 

The  numbers  given  below  are  taken  from  determinations 
made  in  1904 : 


Milligrams  in 

100  grams. 

Grains  in 

i  lb. 

Iron. 

Chalk. 

Iron. 

Chalk. 

Sugar       

— 

— 

— 

— 

Egg-albumen     ... 

— 

i8'8 

— 

I'33 

Cherries  ... 

0'24 

27-2 

O-OI7 

I'93 

Women's  Milk  ... 

0-28  to  o'37 

29-2 

O'02  tO  0'O26 

2-07 

Cow's  Milk 

0-30 

196-3 

0'O2I 

13-94 

Apples     

0-30 

io-6 

0!Q2I 

075 

Rice         

O'S8  to  2'2 

90-6 

0*06  to  o'i5 

6'43 

White  Bread      ... 

0-96 

29-5 

CT07I 

20'8 

Asparagus 

I  '20 

— 

0-08 

— 

Potatoes  

I  -60 

25-0 

o-n 

177 

Rye          

3-2  to  4-2 

527  to  62-4 

0-23  to  0-30    3 

74  to  4-43 

Spinach    ... 

4  to  47 

— 

o'29  to  0-33 

— 

Beef         

47 

8'i 

°'33 

0.57 

Wheat     

4-84 

56-6 

0.34 

4-0 

Egg-yolks 

5  to  ii  *9 

189 

o'35  to  0*84 

I3'4 

COOKING  OF  ANIMAL   FOOD  8  1 

The  quantity  of  iron  in  yolk  of  eggs  varies  with  the  time  of 
year  ;  it  is  greatest  at  the  period  of  hatching. 

Now  that  we  have  considered  separately  the  classes  of 
substances  that  are  required  for  the  nourishment  of  our 
bodies  we  must  deal  with  the  dietetic  value  of  cooking. 
Animal  and  vegetable  food-stuffs  differ  much  when  looked  at 
in  this  respect.  The  preparation  of  animal  flesh  is  not  very 
important  so  far  as  the  nourishing  value  of  the  flesh  is 
concerned.  Raw  minced  beef-steak,  made  palatable  by  the 
addition  of  pepper  and  salt,  is  generally  thought  to  be  very 
nourishing,  and  this  supposition  is  not  unjustified.  We 
certainly  cannot  enjoy  the  raw  flesh  of  fish  or  birds  ;  never- 
theless the  nourishing  value  of  such  flesh  is  not  altered  by 
boiling  or  frying.  In  the  process  of  frying,  however,  the 
heating  of  the  flesh  with  fat  produces  substances  that  have  a 
pleasant  odour  and  an  appetising  flavour,  and  which  therefore 
make  the  consumption  of  the  food  easier.  The  five  following 
analyses  will  elucidate  what  has  been  said  : 


Water.  ProteM,.  Fa«,  ASh. 

Fresh  beef  contains       ......     70*88  22-51  4*52  o'86  1-23 

After  boiling  it  contains            ...     56*82  34*13  7*50  0-40  1-15 

Cooked  beef-steak  contains      ...     55'39  34*23  8'2i  072  1*45 

Uncooked  veal  cutlets  contain...     71-55  20-24  6-38  068  1-15 

Cooked  veal  cutlets  contain     ...     57-59  29-00  11-55  °'43  1'43 

What  especially  strikes  us  in  these  analyses  is  that  boiled 
beef  contains  less  water  than  uncooked  beef.  This  decrease 
in  the  quantity  of  water  is  due  to  the  shrinking  of  the  fibres 
of  the  beef  brought  about  by  the  heating.  But  it  is  much 
more  remarkable  that  the  composition  of  boiled  beef,  or,  as 
we  may  call  it,  soup-beef,  should  be  so  nearly  the  same  as 
that  of  beef-steak  ;  the  percentage  of  albuminoids  (proteids)  is 
indeed  the  same  in  both.  There  is,  however,  a  difference  in 
6 


82  CHEMISTRY  IN   DAILY  LIFE 

the  quantities  of  extractive  substances  ;  in  beefsteak  these 
substances  are  nearly  double  what  they  are  in  boiled  beef. 
In  these  analyses  extractive  substances  mean  those  substances, 
other  than  albuminoids  and  fats,  which  go  into  solution  when 
the  meat  is  boiled  with  water.  Now  these  are  just  the  sub- 
stances that  have  an  appetising  effect  on  the  palate.  Such 
cooked  foods  as  soup-beef,  which  contain  but  little  of  these 
extractives,  taste  insipid,  and  are  not  eaten  with  pleasure. 
Soup-beef,  however,  falls  but  little  behind  other  kinds  of 
animal  food  in  respect  of  nourishing  value  ;  hence,  if  it  is 
not  overboiled,  and  eaten  with  condiments  that  make  it  more 
palatable,  it  is  not  to  be  despised. 

And  this  brings  us  to  inquire  as  to  the  best  way  of  proceed- 
ing when  soup  is  to  be  made  from  meat.  Ought  the  meat  to 
be  put  into  cold  water,  or  into  hot  water  ?  Let  us  answer  the 
question  by  an  experiment. 

We  cover  some  minced  beef  with  cold  water  and  shake 
thoroughly — the  beef  is  minced  so  that  a  large  surface  may 
be  exposed  to  the  action  of  the  water.  We  now  filter  off  the 
solid  matter,  and  thus  obtain  a  clear  liquid  coloured  reddish 
by  the  presence  of  a  small  quantity  of  the  colouring  matters 
of  blood.  On  now  pouring  this  liquid  into  a  beaker  glass  and 
boiling,  we  notice  that  its  colour  changes  to  grey — as  the 
colouring  matter  of  blood  is  unstable  when  heated — and  that 
a  great  deal  of  a  flocculent  solid,  which  is  found  by  experi- 
ment to  be  albumen,  separates  from  the  liquid.  The  cold 
water  has  thus  withdrawn  some  soluble  albumen  from  the 
meat,  and  this  has  of  course  coagulated  when  the  liquid  was 
boiled.  Now  when  soup  is  skimmed  the  albumen  which  has 
become  solid  by  boiling  is  removed  in  the  scum,  and  so  this 
amount  of  nourishment  is  sacrificed  to  the  better  appearance 
of  the  soup. 


SOUP-MAKING  83 

Now  let  us  pour  boiling  water  over  another  portion  of  the 
minced  beef,  and  then  boil  for  a  short  time.  The  meat  very 
soon  becomes  grey,  inasmuch  as  the  colouring  matter  of  blood 
cannot  withstand  the  heat.  We  notice  but  few  flocks  of 
albumen  floating  in  the  liquid,  and  if  we  pour  the  liquid 
through  a  filter  we  obtain  a  clear  fluid  which  does  not  become 
turbid  when  it  is  boiled. 

In  the  latter  part  of  this  experiment  the  boiling  water 
brought  about  the  coagulation  of  the  particles  of  albumen  on 
the  surface  of  the  meat ;  the  fine  pores  of  the  meat  were  thus 
stopped  up,  and  but  very  little  of  the  extractive  substances 
found  their  way  into  the  water. 

The  results  of  everyday  experience  confirm  our  experiment. 
If  one  wants  to  make  a  very  well  flavoured  soup,  the  meat 
must  be  put  into  cold  water,  because  much  extractive  matter 
will  thus  be  taken  out  of  the  meat ;  the  meat  that  remains 
will,  however,  be  disagreeably  tasted  :  but  if  one  wishes  to  get 
palatable  meat  hot  water  must  be  used  ;  in  this  case  the 
flavour  of  the  soup  will  not  be  very  good. 

Generally  speaking  soups  are  required  to  be  pleasant  to  the 
palate,  rather  than  to  possess  a  high  nutritive  value  ;  the 
results  of  the  analysis  of  a  soup,  prepared  in  the  ordinary  way 
from  500  grams  [about  I  lb.]  of  beef  and  190  grams 
[about  I  lb.]  of  veal  bones,  will  show  that  this  requirement  is 
fulfilled. 

Water     95>J8  per  cent. 

Proteids rig  „  „ 

Fats        1-48  „  „ 

Extractive  substances 1*83  „  „ 

Ash         0-32  „  „ 

Water  is  the  chief  constituent  of  this  soup.  The  proteids 
consist  chiefly  of  gelatin,  as  the  albuminoids  have  been 
coagulated  by  the  heating  and  removed  by  skimming.  The 


84  CHEMISTRY   IN    DAILY   LIFE 

quantity  of  fat  is  of  course  inconsiderable.  Still  we  consume 
soups  willingly,  and  experience  teaches  us  to  ascribe  to  them 
a  stimulating  action  on  the  nervous  system  ;  this  action  must 
be  regarded  as  due  to  the  extractives,  and  also  to  the  potash 
salts,  they  contain.  About  half  of  the  ash  of  the  soup  referred 
to  in  the  foregoing  analysis  consisted  of  potash,  and  about 
one-fourth  of  phosphoric  acid.  The  addition  of  herbs  to 
soups  serves  of  course  only  to  improve  the  flavour. 

The  importance  of  boiling,  baking,  etc.,  is  very  different  in 
the  case  of  vegetable  foods  from  what  it  is  when  animal  food 
is  concerned.  Most  vegetable  substances,  except  fruits,  are 
too  hard  to  be  eaten  uncooked,  and  their  organised  tissues,  to 
which  they  owe  their  existence,  must  be  broken  up  by  cook- 
ing before  we  can  use  them  as  foods. 

The  different  kinds  of  grains,  which  are  the  chief  sources  of 
our  vegetable  foods,  must  be  broken  up  and  freed  from  their 
husks  by  grinding  in  order  that  we  may  get  at  the  flour 
within.  But  even  then  the  flour  is  not  suitable  for  human 
food,  as  the  raw  starch  granules  surrounded  by  their  cell- 
coverings  are  only  very  slowly  attacked  by  the  digestive 
fluids.  Quite  a  different  state  of  affairs  is  brought  about  by 
heating  the  flour  with  water ;  the  coverings  of  the  cells 
are  burst  open,  the  starch  escapes  and  passes  into  the  pasty 
condition,  when  it  is  easily  digested  (see  p.  67).  The  same 
purpose  is  served  by  the  baking  of  bread,  which  process  also 
brings  about  that  peculiar  sponginess  of  texture  to  which 
bread  owes  its  great  digestibility. 

When  flour  is  stirred  up  with  water  a  very  tough  dough  is 
obtained,  because  of  the  gluten  in  the  flour.  Gluten  is  a  proteid 
substance  contained  in  flour  which  becomes  of  a  glue-like  con- 
sistence (hence  the  name)  when  moistened.  If  such  dough 
is  baked  without  further  treatment  a  hard  mass  is  obtained 


BREAD-MAKING  85 

somewhat  resembling  ship  biscuits.  But  if  the  dough  is 
allowed  to  stand  for  some  time  it  undergoes  change ;  yeast- 
cells  fall  into  it  from  the  air,  and  these  cause  the  sugar  of  the 
flour  to  ferment  (a  process  to  be  dealt  with  immediately)  ;  the 
bacilli  which  cause  lactic  fermentation  (see  p.  57)  also  find 
their  way  into  the  dough,  and  produce  lactic  acid  from  the 
sugar.  The  lactic  acid — and  other  acids  chemically  like  it 
which  are  also  produced  in  the  dough — then  acts  on  the  starch 
to  produce  glucose,  so  that,  even  if  the  flour  originally  con- 
tained but  little  sugar,  the  yeast  finds  sufficient  sugar  to 
ferment. 

Fermentation  caused  by  yeast,  by  which  process  all 
spirituous  drinks  (to  be  considered  in  detail  in  the  next 
lecture)  are  prepared,  consists  in  the  transformation  of  sugar 
(glucose)  into  carbonic  acid  gas  and  spirit,  or,  as  the  latter 
substance  is  called  in  chemistry,  alcolwl.  The  process  may  be 
represented  as  follows  : 

[One  molecule  of  grape  produces  two  mole-  and  two  molecules 

sugar,  consisting  of  cules  of  alcohol,  each  of  carbonic  acid, 

consisting  of  each  consisting  of 

6  atoms  of  carbon  2  atoms  of  carbon  I  atom  of  carbon 

12  atoms  of  hydrogen        6  atoms  of  hydrogen 
6  atoms  of  oxygen  i  atom  of  oxygen  2  atoms  of  oxygen. 

The  process  is  presented  more  shortly  thus  : 

CfiH12O6  2  C2H8O      +  2  CO2. 

i  molecule  glucose  -  2  mols.  alcohol  2  mols.  carbonic  acid. 

One  molecule  of  sugar  (glucose)  is  transformed  into  two 
molecules  of  alcohol  and  two  of  carbonic  acid  gas.  The 
carbonic  acid  gas  is  produced  in  the  dough,  and,  as  it  cannot 
escape  from  the  pasty  mass,  it  causes  the  dough  to  rise — that 
is,  to  swell  up  in  bubbles.  When  the  dough  is  put  into  the 
oven  the  alcohol  begins  to  evaporate,  and  this  process  also 
tends  to  loosen  the  bread  and  make  it  spongy.  The  heat 


86  CHEMISTRY   IN    DAILY   LIFE 

also  breaks  up  the  cells  of  the  moist  starch  granules  which  at 
once  begin  to  become  pasty.  The  outer  portions  of  the 
bread  become  so  hot  that,  when  the  bread  is  sufficiently 
baked,  part  of  the  starch  is  converted  into  dextrin  (see  p.  71)  ; 
and  as  dextrin  has  a  somewhat  pasty  consistence,  the  starch 
granules,  and  other  similar  constituents  of  the  bread,  adhere 
together  and  form  the  crust  that  we  are  accustomed  to  see 
on  the  outside  of  loaves  of  bread. 

If  bread  dough  is  allowed  to  stand  in  the  air  it  becomes 
sour  because  of  the  formation  in  it  of  lactic  acid  and  other 
similar  acids. 

It  takes  a  considerable  time  for  dough  to  ferment  and 
become  sour  by  the  action  of  the  yeast  cells  and  bacilli  that 
may  fall  into  it  from  the  air  ;  but  if  fresh  dough  is  mixed  with 
a  little  dough  that  has  become  sour  by  standing  in  the  air 
fermentation  processes  go  on  rapidly,  as  it  is  known  that 
yeast  cells  and  bacilli  increase  in  number  with  extraordinary 
rapidity.  When  therefore  one  batch  of  dough  has  fermented, 
a  small  quantity  of  it  is  set  aside  in  order  to  start  the 
fermentative  changes  in  the  next  batch.  The  flavour  of  sour 
dough  is  communicated  to  bread  baked  with  such  dough. 
Nowadays  only  black  bread  is  made  with  sour  dough,  and  the 
peculiar  flavour  of  this  bread  is  due  to  the  dough  used  in 
making  it.  For  making  white  bread  it  is  preferred  to  use 
fresh  yeast;  this  yeast  was  formerly  obtained  from  the 
breweries,  but  to-day  it  is  prepared  for  baking  purposes  by  a 
special  process.  We  shall  leave  the  further  consideration  of 
this  subject  until  we  are  speaking  of  fermented  drinks,  when 
we  shall  have  a  better  grasp  of  the  facts  that  are  needed  for 
its  elucidation. 

There  are  several  substances  which  are  used  as  substitutes 
for  yeast  in  causing  dough  to  rise.  Carbonate  of  ammonia  is 
sometimes  used  in  household  baking,  under  the  name  of 


BAKING   POWDERS  87 

salts  of  hartshorn.  This  substance  is  composed  of  ammonia, 
which  is  a  basic  gas,  and  carbonic  acid,  which  is  an  acid  gas 
(see  p.  49)  ;  the  substance  is  a  solid,  but  at  the  temperature  of 
the  baking  oven  it  is  resolved  into  its  gaseous  constituents, 
and  these  gases  cause  the  dough  to  rise.  Potashes,  which  is 
carbonate  of  potash  (see  p.  45),  is  also  used.  The  solid  salt 
is  not  decomposed  by  heat,  but  it  gives  off  carbonic  acid  gas 
if  it  is  mixed  with  sour  dough.  If  the  dough  contains  lactic 
acid  this  acid  decomposes  the  carbonate  of  potash,  forming 
lactate  of  potash,  and  carbonic  acid  gas  which  permeates  the 
dough  and  causes  it  to  rise.  The  action  of  this  salt  is 
effectual  only  when  dough  contains  a  considerable  quantity  of 
acid,  for  only  then  is  sufficient  carbonic  acid  gas  produced  to 
bring  about  the  proper  rising  of  the  dough. 

Reflection  will  show  that  the  process  of  raising  dough  by 
fermentation  must  be  accompanied  by  the  loss  of  some 
nutritive  substances,  because  fermentation  always  means 
destruction  of  sugar.  Following  Liebig,  attempts  have  been 
made  to  obviate  this  loss  by  using  baking  powders  whereby 
sufficient  carbonic  acid  should  be  produced  in  the  dough  to 
cause  it  to  rise  and  to  become  spongy. 

Horsford's  baking  powder,  for  instance,  which  is  much 
used,  is  a  mixture  of  bicarbonate  of  soda  and  acid  phosphate 
of  lime  ;  when  this  is  kneaded  into  dough,  the  moisture  in  the 
dough  induces  a  reaction  between  the  constituents  of  the 
baking  powder  whereby  carbonic  acid  gas  is  produced  in  such 
quantity  that  the  dough  becomes  loose  and  spongy  and  ready 
for  putting  into  the  baking  oven.  Another  baking  powder 
consists  of  a  mixture  of  tartaric  acid  and  carbonate  of  soda 
with  powdered  starch.  The  action  of  this  powder  is  similar 
to  that  of  Horsford's  powder  ;  the  starch  is  quite  super- 
fluous. 

It  remains  now  to  say  a  word  or  two  on  the   boiling  of 


88  CHEMISTRY   IN    DAILY   LIFE 

potatoes.  Raw  potatoes  are  much  too  hard  to  be  consumed 
as  food.  Their  hardness  is  caused  by  the  husks  which 
enclose  the  starch  granules;  these  husks  are  so  connected 
together  as  to  form  what  may  be  called  the  skeleton  of  the 
potato.  This  skeleton  is  so  compact  that  the  starch  granules 
cannot  be  disintegrated  by  the  digestive  fluids  in  the  human 
stomach.  But  when  potatoes  are  boiled  the  husks  are  burst 
off  from  the  starch  granules,  and  these  granules  assimilate 
ivater  and  pass  into  that  pasty  state  wherein  the  digestive 
fluids  readily  act  on  them  with  the  production  of  sugar 
(see  p.  69).  The  sugar  thus  finds  its  way  into  the  system, 
and  is  used  for  nourishing  the  body. 

It  will  be  easy  for  you  to  apply  the  principles  laid  down 
and  illustrated  in  this  lecture  to  the  boiling  and  baking,  etc., 
of  other  kinds  of  food-stuffs  besides  those  we  have  especially 
mentioned  here. 


LECTURE   V 

Quantity  of  food  that  must  be  consumed,  and  nutritive  values  of  the  chief 
foods — Fermentation— Wine — Cider  and  perry — Champagne — Mead 
— Koumiss — Beer— Malt — Spirits — Dry  yeast  [German  yeast] — 
Brandy — Potato  spirit — Vinasse — Spirit  refining — Absolute  alcohol — 
Methylated  alcohol — Liqueurs. 

WE  come  now  to  the  important  question,  how  much  must  a 
man  eat  to  keep  himself  in  full  vigour?  We  know  already 
that  he  ought  to  consume  a  mixed  diet,  consisting  of  both 
nitrogenous  substances  (albuminoids)  and  non-nitrogenous 
substances  (fats  and  carbohydrates). 

The  greater  or  less  abstinence  of  the  vegetarians  cannot 
make  us  forget  this  aspect  of  the  question  of  food.  As  these 
people  reject  all  albuminoids  which  are  of  animal  origin,  they 
must  derive  the  nitrogenous  food  which  they  require  altogether 
from  plants.  The  analyses  which  have  been  put  before  you 
(p.  68)  show  that  the  proportion  of  the  two  kinds  of  food  in 
plants  is  unsuitable,  inasmuch  as  the  quantity  of  carbo- 
hydrates so  greatly  preponderates  that  if  sufficient  albuminoid 
substances  are  to  be  obtained  from  that  source  it  is  necessary 
to  take  into  the  body  at  the  same  time  far  more  than  enough 
useless  ballast  in  the  form  of  carbohydrates.  Of  course  it  may 
be  demonstrated  that  a  man  can  exist  on  vegetable  diet  only. 
But  the  argument  that  such  graminivorous  animals  as  the 
horse  or  the  elephant  become  very  vigorous  on  a  purely 
vegetable  diet  is  not  to  'the  point,  because  nature  has 


90  CHEMISTRY   IN    DAILY   LIFE 

provided  such  animals  with  very  long  intestines  for  the 
better  absorption  of  this  diet.  Many  graminivorous  animals 
have  also  several  stomachs,  and  they  masticate  their  food 
repeatedly. 

While  it  is  possible  for  the  vegetarian  to  feed  himself  suf- 
ficiently by  this  method  without  too  much  trouble,  it  seems 
that  a  purely  albuminoid  diet  can  scarcely  suffice  for  the 
nourishment  of  human  beings.  This  is  made  evident  in  the 
cases  of  diabetic  patients  ;  such  people  ought  not  to  consume 
anything  of  vegetable  origin,  but  it  is  impossible  for  them  to 
continue  such  a  diet  for  a  length  of  time.  The  almost  total 
denial  to  them  of  food  containing  starchy  matter  is  a  source 
of  lasting  discomfort,  and  yet  this  is  the  only  way  of  prevent- 
ing those  serious  consequences  which  are  otherwise  certainly 
induced  by  this  disease. 

Many  investigations  have  been  carried  out  by  Voit  and 
Pettenkofer  with  regard  to  the  quantity  of  nourishment  that 
is  required  by  a  man  daily.  We  shall  quote  a  few  of  the 
results. 

An  efficient  worker  requires  daily,  when  he  is  working, 

137  grams  [about  2,100  grains]  albumen,  173  grams  [about  2,650 
grains]  fats,  and  352  grams  [about  5,400  grains]  carbohydrates  (starch  or 
sugar). 

The  following  numbers  were  brought  out  in  the  case  of  a 
young  physician  : 

127  grams  [about  1,950  grains]  albumen,  89  grams  [about  1,370  grains] 
fats,  and  362  grams  [about  5,600  grains]  carbohydrates. 

The  following  numbers  represent  mean  values  : 

118  grams  [about  1,800  grains]  albumen,  88*4  grams  [about  1,360 
grains]  fats,  and  392*3  grams  [about  6,040  grains]  carbohydrates. 

This  quantity  of  albumen  corresponds  to  18*3  grams  [about 


QUANTITY  OF  FOOD  REQUIRED  QI 

282  grains]  nitrogen,  which  is  the  quantity  contained  in  the 
following  weights  of  different  food-stuffs  : 

Grams  =     Lbs.  Grams     =     Lbs. 

Cheese     ...  272  o'6  Cream             ...  2,650        S'4 

Peas          ...  520  1*15  Milk     2,905         6*4 

Lean  flesh  538  ri8  Potatoes          ...  4,575  ro'i 

Wheat  flour  796  1*75  Bacon  ...         ...  4,796  io'57 

Eggs  *      ...  905  2  White  Cabbage  7,625  i6'8 

Black  Bread  1,430  3*15  Beer     17,000  37*5 

Rice           ...  1,868  4*12 

The  amount  of  carbon  required  daily  by  a  man  is  328 
grams  [about  5,050  grains] ;  this  quantity  is  contained  in  the 
following  weights  of  different  food-stuffs: 

Grams     =     Lbs.  Gtams  =    Lbs. 

Bacon        ...      450  0*99  Eggs 2,231  4-91 

Wheat  flour      824  i'8i  Lean  flesh     ...  2,620  577 

Rice           ...      896  1*97  Potatoes        ...  3,124  6*89 

Peas           ...      919  2*03  Milk...           ...  4,652  10*25 

Cheese      ...  1,160  2*56  WhiteCabbage  9,318  20*54 

Black  Bread  1,346  2*97  Beer 13,160  29^01 

Cream       ...  1,410  3*13 


If  we  weigh  out  the  quantity  of  carbon  that  our  daily  need 
demands,  say  in  the  form  of  wood  charcoal,  we  are  astonished 
to  find  that  more  carbon  is  required  for  twenty-four  hours' 
heating  of  a  man — if  one  may  use  such  an  expression — than 
for  heating  a  small  stove  during  the  same  time.  It  requires 
much  more  carbon  than  we  generally  suppose  to  maintain  a 
human  body — weighing,  say,  70  kilos,  [about  n  stones] — 
constantly  at  the  temperature  of  37°  C.  [98-5°  F.]  and  to  keep 
it  in  vigour.  If  we  think  of  the  human  body  as  a  machine, 

*  A  question  is  often  asked  as  to  the  relative  nutritive  values  of  eggs 
and  meat ;  the  numbers  in  the  tables  show  that,  on  an  average,  from  18 
to  20  eggs  are  equal  to  i  kilo,  [about  2\-  Ibs.]  of  meat. 


92  CHEMISTRY   IN   DAILY   LIFE 

we  must  remember  that,  like  the  bodies  of  other  animals,  it 
differs  from  ordinary  machines  in  that  the  substance  of  all 
the  organs  is  constantly  changing,  whereas  the  material  of  a 
machine  remains  unchanged. 

If  the  foregoing  numbers  are  examined  more  closely  they 
are  found  to  confirm  the  ordinary  experience  of  life  for  the 
most  part,  but  in  some  particulars  they  go  against  our  pre- 
conceived opinions.  A  diet  of  bacon  and  peas  is  generally 
thought  to  be  very  nourishing,  and  our  tables  show  that  we 
need  not  consume  very  much  of  these  two  together  to  supply 
our  daily  requirements.  But  if  we  desire  to  obtain  sufficient 
nourishment  from  beer  alone,  the  tables  show  that  the 
nutritive  value  of  this  drink  is  so  small  that  17  litres  [3! 
gallons]  of  it  are  required  to  furnish  sufficient  albuminoid 
substances,  and  13  litres  [2  gallons]  to  furnish  sufficient 
carbon  for  a  day's  requirements.  Beer  indeed  can  scarcely 
be  called  a  food  in  the  strict  sense  of  that  term  ;  it  must 
rather  be  regarded  as  a  nourishing  beverage,  for  the  regular 
consumption  of,  say,  a  litre  [if  pints]  of  beer  per  day  will 
supply  only  about  one-seventeenth  of  the  total  nourishment 
that  we  require. 

Black,  or  rye,  bread  is  the  most  perfect  of  all  the  foods 
mentioned  in  the  preceding  tables,  for  about  ij  kilos.  [3^  Ibs.] 
of  that  substance  suffice  to  supply  the  total  daily  needs  of  a 
man.  This  explains  the  fact  that  labourers  are  very  vigorous, 
although  they  are  not  so  well  nourished  as  the  better-to-do 
classes,  who  regularly  eat  meat.  It  is  also  easy  to  under- 
stand that,  because  of  the  constant  use  of  his  muscular 
activity,  a  labourer  may  possess  a  greater  physical  energy 
than  those  who  are  much  better  off  in  so  far  as  change  of  diet 
is  concerned. 

The  numbers  which  have  been  given  exhibit  the  minimum 


FERMENTED  LIQUORS  93 

quantities  of  nourishment  required  for  the  maintenance  of  the 
life  of  a  man  in  full  work.  If  any  one  falls  below  this  he 
gradually  collapses  ;  even  those  who  are  especially  abstemious 
must  consume  at  least  this  minimum  quantity.  Generally 
speaking  a  man  eats  much  more  than  this,  as  it  is  quite  im- 
possible to  maintain  the  theoretically  correct  proportion  of 
the  different  kinds  of  food,  and,  moreover,  habit  plays  a  very 
important  part  in  the  matter. 

The  body  assimilates  what  it  requires  for  its  existence,  and 
what  remains  unused  is  excreted. 

The  statement  we  have  made  that  a  man  can  exist  on 
ij  kilos.  [3^  Ibs.]  of  rye  bread  consumed  daily  is  of  course 
purely  theoretical,  inasmuch  as  no  one  is  able  to  live  on  rye 
bread  alone  for  a  length  of  time.  But  if  the  bread  is  made 
more  palatable  by  the  addition  of  butter,  sausages,  or  the  like, 
and  if  some  other  food  is  substituted  every  day  for  part  of  the 
bread,  such  a  beverage  as  warm  coffee  being  also  consumed, 
then  the  statement  expresses  what  actually  happens  with 
many  people. 

Let  us  now  consider  fermented  liquors  more  fully  than  we 
did  in  the  last  lecture. 

If  liquids  that  contain  sugar,  but  not  very  large  quantities 
of  sugar,  are  exposed  to  the  air  they  slowly  undergo  a  very 
marked  change  in  their  properties,  and  this  change  is  accom- 
panied by  the  evolution  of  gas  and  the  formation  of  a  deposit 
which  is  known  by  the  name  of  yeast. 

The  most  striking  feature  of  the  change  is  that  the  liquids 
have  become  intoxicating.  The  process  itself  is  known  as 
fermentation^  and  the  liquids  that  are  produced  are  called 
fermented  liquors. 

Very  concentrated  sugar  solutions  do  not  undergo  this 
process  ;  such  liquids  have  indeed  preservative  properties,  and 


94  CHEMISTRY   IN   DAILY  LIFE 

these  properties  are  taken  advantage  of  in  the  preparation  of 
preserved  fruit.* 

It  has  already  been  pointed  out  (p.  57)  that  all  processes 
of  fermentation  are  caused  by  exceedingly  minute  living 
organisms  which  are  present  everywhere  in  the  air.  That 
organism  which  especially  causes  the  change  of  sugar  into 
alcohol  and  carbonic  acid  is  called  Saccliaromyces  cerevisice!\ 

The  juice  obtained  by  pressing  grapes — called  must — is  the 
most  easily  fermented  of  all  liquids.  This  juice  contains 
the  directly  fermentable  sugar,  glucose,  and  also  all  those 
substances  which  yeast  requires  for  its  growth  ;  for  as 
yeast  is  a  living  organism  it  can  only  thrive  under  definite 
conditions — for  instance,  in  the  presence  of  certain  inorganic 
salts. 

The  liquid  which  is  finally  obtained  by  this  fermentation  is 
called  wine. 

We  can  tell  from  their  flavour  that  wines  made  from 
different  kinds  of  grapes  contain  very  different  quantities  of 
sugar  ;  the  quantity  of  alcohol  in  wines  also  varies,  the  upper 
limit  being  determined  by  the  fact  that  when  the  quantity  in 
a  fermenting  liquid  reaches  about  16  per  cent,  by  volume  the 
yeast  dies.  The  following  table,  however,  shows  that  some 
wines  contain  much  more  than  16  per  cent,  of  alcohol  by 
volume.  To  such  wines  alcohol  has  been  added.  The  addi- 
tion of  alcohol  is  made  partly  for  the  purpose  of  making  the 

*  It  should  be  noted  that  some  sugars  do  not  undergo  fermentation, 
and  that  cane  sugar  and  milk  sugar  belong  to  those  which  cannot  be 
fermented  directly.  But  when  fermentation  is  set  up  in  substances 
contained  in  a  solution  in  which  these  sugars  are  present  the  sugars 
themselves  are  changed  into  fermentable  sugars  (see  forward). 

t  We  are  not  concerned  here  with  a  purely  chemical  reaction,  but  with 
changes  that  are  connected  with  the  life-processes  of  certain  moulds  ; 
small  quantities  of  other  substances  besides  the  main  products  are 
formed  in  these  changes. 


WINES  95 

wine  keep  better,  and  partly  to  give  that  particular  flavour 
which  the  public  are  accustomed  to  connect  with  the  name  of 
the  wine  in  question. 

ALCOHOL.  SUGAR. 

Volume  per  cent.        Per  cent. 

Silesian  wine 5-5 

Markobrunner  (1882)            ...         ...         ...  7-17 

Liebfraumilch  (1875) n'55 

Voslauer  Goldeck  (1868)      10-28 

St.  Julien  (1865)         9-28 

Chablis  (1862) 9-30 

Malmsey          7-50              36*40 

Samos  ...         ...         ...         ...         ...         ...  14*96                7'68 

Tokay,  selected          1076             25*34 

Tokay,  selected  1 1 14-84               8'2O 

Port       19-82               4-82 

Madeira           19-12               3-46 

Malaga 15-12              15-50 

Sherry 21*22               2*04 

This  table,  which  is  made  somewhat  lengthy  because  of  the 
many  different  kinds  of  wine  we  meet  with,  shows  that  the 
sugar  in  wines  made  from  very  sweet  grapes  is  not  wholly 
converted  into  alcohol,  for  the  reason  already  mentioned, 
while  there  is  no  sugar  in  wines  that  are  made  from  grapes 
poor  in  sugar.  The  sugarless  wines  are  suitable  for  diabetic 
patients. 

That  fine  aroma,  which  always  becomes  more  apparent 
as  wines  age,  called  the  bouquet  of  wines,  is  due  to  chemical 
compounds,  all  of  which  cannot  be  accurately  defined, 
but  among  which  are  to  be  found  certain  etJiereal  salts  of 
organic  acids,  a  class  of  compounds  the  composition  of  which 
cannot  be  explained  without  a  more  profound  chemical 
knowledge.  These  compounds  are  formed  in  wines  by  the 
agency  of  bacteria.  Small  quantities  of  bacteria  have  been 
found  in  wines  kept  in  corked  bottles  for  as  long  as  forty 
years. 


96  CHEMISTRY   IN   DAILY  LIFE 

Cider  and  perry  are  alcoholic  liquids  prepared  by  pressing 
apples  and  pears  and  allowing  the  musts  to  ferment.  As  the 
juices  of  these  fruits  contain  but  little  sugar  the  liquid 
obtained  by  the  fermentation  of  these  juices  would  be  very 
poor  in  alcohol ;  sugar  is  therefore  added  to  the  musts  before 
fermentation  begins,  and  a  proper  amount  of  the  most 
important  constituent  is  thus  insured  in  the  fermented 
products.  When  currants  or  similar  slightly  sweet  fruits  are 
made  use  of,  the  addition  of  sugar  is  absolutely  necessary  if  a 
drink  is  to  be  obtained  with  anything  like  a  fair  amount  of 
alcohol  in  it. 

Beverages  free  from  alcohol  are  now  prepared  in  con- 
siderable quantities,  by  boiling  the  peelings  of  apples  with 
water — the  apple-peelings  are  imported  for  the  most  part  from 
America,  where  they  are  dried  before  being  shipped — and 
impregnating  the  liquid  with  carbonic  acid  gas. 

Champagne  is  prepared  from  grape-musts  in  many  countries. 
The  name  is  derived  from  the  district  of  Cltampagne,  where 
this  wine  has  been  prepared  certainly  since  the  middle  of  the 
eighteenth  century.*  Champagne  is  made  by  pouring  the  must, 
after  the  first  energetic  fermentation  is  over,  into  bottles,  which 
are  then  tightly  corked.  As  the  after-fermentation  proceeds 
carbonic  acid  gas  is  generated,  and  as  this  gas  cannot  escape  it 
gradually  produces  a  considerable  pressure  inside  the  bottles. 
As  many  impurities  are  gradually  deposited  while  the  wine  is 
fermenting  in  the  bottles,  the  custom  is  to  set  the  bottles  on 
their  heads  as  the  second  fermentation  is  proceeding,  and  to 
give  them  a  twisting  movement  from  time  to  time ;  a  work- 

*  The  word  sack  [sekt  in  German],  which  is  so  often  used  by  Falstaff, 
means  what  we  now  call  sherry.  The  actor  Devrient  brought  the  word 
sekt  into  fashion  [in  Germany]  as  a  name  for  champagne  about  the  year 
1820 


CHAMPAGNE  97 

man  then  opens  the  bottle,  and  the  first  portion  of  liquid  that 
is  driven  out  carries  these  impurities  with  it.  The  bottles 
are  then  turned  round,  filled  up  with  the  liqueur,  and 
corked.  The  bottles  are  kept  for  some  time  before  they  are 
sent  into  the  market.  When  the  wire  that  holds  the  cork  is 
removed  the  accumulated  carbonic  acid  forces  out  the  cork 
with  a  loud  sound. 

The  composition  of  the  liqueurs  on  which  the  flavour  of  the 
finished  wine  so  much  depends  is  kept  secret  by  the  manu- 
facturers. 

In  former  days  about  one-fourth  of  the  bottles  were 
broken  during  the  manufacture  by  the  great  outward  pressure 
of  the  carbonic  acid  ;  but  the  glass  industry  is  so  much 
improved  that  not  more  than  one  bottle  in  a  hundred  bursts 
nowadays. 

It  is  evident  that  wherever  wine  is  made  champagne  might 
be  manufactured  ;  but  the  minute  carefulness  required  in  the 
processes  must  always  prevent  good  champagne  from  be- 
coming cheap,  as  we  see  in  the  prices  of  the  best  brands. 
Notwithstanding  this  we  know  that  effervescing  wines  can  be 
bought  to-day  at  a  very  low  price  ;  but  these  liquors  are  not 
made  in  the  same  way  as  champagne,  and  indeed  they  have 
nothing  in  common  with  genuine  champagne  except  the 
name.  The  manufacture  consists  in  forcing  carbonic  acid — 
in  the  same  way  as  is  practised  in  making  soda  water — into 
light  white  wines  which  have  been  sweetened,  if  necessary,  by 
adding  sugar ;  when  this  is  done  the  champagne  is  ready  for 
the  market. 

A  bottle  of  soda  water  can  be  bought  to-day  for  a  few 
pence  ;  hence  to  charge  wine  with  carbonic  acid,  and  so  to 
change  it  into  so-called  champagne,  can  cost  but  little,  and 
the  product  can  be  sold  very  cheaply. 

While  the  inhabitants  of  countries  where  the  vine  flourishes 
7 


98  CHEMISTRY  IN   DAILY  LIFE 

have  been  acquainted  with  wine  since  the  earliest  times, 
because  its  preparation  almost  forced  itself  on  their  notice, 
people  living  in  more  northern  climes  found  other  methods 
for  obtaining  alcoholic  liquors,  the  use  of  which  when 
once  acquired  seems  never  to  have  been  abandoned  by 
any  race. 

The  dwellers  in  the  lands  north  of  the  Alps,  where  the  vine 
was  introduced  when  these  countries  were  conquered  by  the 
Romans,  were  long  ago  acquainted  with  mead.  This  drink  is 
easily  made ;  the  starting-point  is  honey,  which  is  very  rich 
in  sugar.  The  honey  of  bees  does  not  ferment  of  itself 
because  it  is  too  concentrated ;  but  if  it  is  diluted,  and 
exposed  to  air,  fermentation  is  brought  about  by  the  yeast 
which  falls  into  it,  and  the  intoxicating  liquor  called  mead 
is  produced.  To-day  this  drink  is  as  good  as  forgotten  ; 
its  taste,  as  one  may  easily  convince  oneself,  is  not  very 
agreeable. 

The  drinking  of  koumiss,  which  is  fermented  mares'  milk, 
has  probably  persisted  since  early  days ;  but  this  drink  is 
found  only  in  Central  Asia,  whence  it  has  never  spread.  We 
must  say  a  little  about  the  production  of  this  drink,  because 
when  milk  stands  in  the  air  in  our  climate  it  is  not  changed 
by  yeast  into  an  intoxicating  liquid,  but  it  becomes  sour  by 
the  conversion  of  its  sugar  into  lactic  acid  through  the  agency 
of  the  lactic  ferment  (see  p.  5). 

If  milk  is  diluted  with  about  ten  times  its  volume  of  water, 
and  some  koumiss  is  then  added  to  the  diluted  milk,  the  lactic 
ferment  in  the  koumiss  quickly  causes  the  conversion  of 
a  part  of  the  milk-sugar  into  lactic  acid,  and  this  acid  then 
reacts  with  the  rest  of  the  milk-sugar  and  transforms  that 
into  a  sugar  which  is  directly  fermentable  (see  the  footnote, 
p.  94),  and  then  fermentation  into  alcohol  and  carbonic  acid 
begins. 


BEER  99 

Cows'  milk  can  be  converted  into  an  intoxicating  liquor  by 
a  similar  process  ;  and  the  preparation  of  this  liquid  has  been 
attempted  in  many  places  on  a  large  scale,  but  the  manu- 
facture has  been  given  up,  as  the  taste  of  the  drink  does  not 
seem  to  suit  the  palates  of  Europeans. 

People  living  in  European  countries  where  the  vine 
will  not  flourish  have  learnt,  in  the  course  of  time,  to 
manufacture  beer  in  place  of  mead  and  similar  drinks  ;  and 
the  taste  of  beer  is  so  much  better  than  that  of  the  last- 
mentioned  alcoholic  liquids  that  beer  has  driven  these  entirely 
out  of  use. 

The  preparation  of  beer  rests  on  the  following  principles. 
When  seeds  are  placed  in  moist  earth  they  soon  put  forth 
rootlets  and  then  leaves.  The  rootlets  are  not,  however, 
at  once  able  to  carry  nourishment  {to  the  leaves,  and  so 
the  supplies  of  starch  flour  and  albumen  stored  in  the  seeds 
are  drawn  upon.  As  germination  proceeds  a  substance  is 
formed  which  converts  the  starch  into  sugar  and  dextrin, 
and  the  albuminoids  at  the  same  time  become  soluble. 
The  substances  held  in  reserve  in  the  seeds  having  thus 
become  soluble  serve  to  nourish  the  plantlet  until  the  roots 
have  strengthened  sufficiently  to  take  this  duty  on  themselves. 

Experience  has  shown  that  barley  grains  are  the  most 
suitable  of  all  cereals  for  beer  making,  the  proper  understand- 
ing of  which  process  requires  us  to  bear  in  mind  what  has 
just  been  said.  Certain  kinds  of  beer — Berlin  Weissbier,  for 
instance — can  be  made  from  wheat. 

We  shall  confine  our  attention  to  beer  made  from  barley, 
as  that  beer  is  much  more  generally  consumed  than  any 
other,  and  it  will  then  be  easy  to  understand  the  preparation 
of  other  kinds  of  beer. 


100  CHEMISTRY  IN   DAILY  LIFE 

For  the  purpose  of  making  beer  barley  is  steeped  in  water 
and  is  then  placed  in  a  cellar  kept  not  too  cold.  The  result 
is  that  the  barley  germinates  without  being  put  into  the 
earth  ;  little  roots  are  pushed  forth,  and  the  substance — 
called  diastase — which  has  the  property  of  changing  starch 
into  sugar,  is  formed  in  the  barley.  The  albuminoids  in  the 
barley  at  the  same  time  become  soluble  in  water. 

When  the  rootlets  have  grown  as  much  as  experience  has 
shown  to  be  proper  the  barley  is  dried,  and  the  substance  so 
obtained  is  called  malt.  The  drying  may  be  done  in  an  open 
place,  but  it  is  generally  carried  out  by  maltsters  in  kilns — 
that  is,  in  highly  heated  apartments.  The  higher  the 
temperature  employed  in  the  kilns  the  greater  is  the  quantity 
of  brown  substances  produced  in  the  malt,  and  therefore  the 
darker  is  the  colour  of  the  beer.  If  very  dark-coloured  beer 
is  to  be  made  a  portion  of  the  malt  is  finally  roasted  in  an 
apparatus  like  a  coffee-roaster  (cf.  p.  71). 

The  malt  is  now  crushed,  and  it  is  then  run  into  tuns, 
where  it  is  treated  with  water  kept  at  50°  to  70°  C.  [120°  to 
170°  F.],  because  the  conversion  of  starch  into  sugar  and 
dextrin  proceeds  most  rapidly  at  this  temperature.  The 
liquor  obtained  by  this  process  of  mashing  is  called  wort ;  it 
contains  much  sugar.  But  if  this  liquor  were  fermented 
without  any  other  treatment  a  very  disagreeable  beer  would 
be  obtained.  It  has  long  been  known  that  if  a  drink  with  a 
pleasant  flavour  is  to  be  obtained  from  malt  some  bitter 
substance  must  be  added.  Hops  are  used  everywhere  for 
this  purpose ;  they  have  been  grown  on  the  Rhine  since  the 
ninth  century.  Oak  wood  was  used  at  one  time  in  some 
parts  of  Germany  for  imparting  a  bitter  flavour  to  beer  ;  but 
such  beer  would  not  find  favour  nowadays. 

The  wort  is  boiled  with  hops  ;  in  this  process  some  water 
is  evaporated,  and  the  wort  thus  becomes  slightly  more 


BEER  101 

concentrated.  The  wort  is  now  cooled  by  exposure  in  fiat 
vessels,  the  process  being  hastened  by  mechanical  contriv- 
ances. If  the  cooling  is  not  done  rapidly  there  is  a  danger 
of  the  fermentation  proceeding  in  a  wrong  direction  ;  for  the 
lactic  fermentation,  that  we  have  often  spoken  of,  is  liable  to 
begin  between  25°  and  30°  C.  [77°  and  86°  F.],  and  if  this 
occurs  the  beer  is  spoilt.  The  last  process  consists  in  allow- 
ing the  liquid,  cooled  to  the  proper  temperature,  to  ferment 
in  large  vats,  after  some  yeast  taken  from  a  former  fermenta- 
tion has  been  added  to  it. 

If  the  liquid  were  allowed  to  stand  until  sufficient  yeast  had 
fallen  into  it  from  the  air  the  process  of  fermentation  would 
be  very  slow  and  very  uncertain  ;  but  if  some  yeast  is  added 
this  yeast  very  quickly  grows  in  the  liquid,  inasmuch  as  it 
finds  there  everything  that  is  required  for  its  nourishment. 
If  the  fermentation  is  allowed  to  proceed  at  a  temperature  of 
12°  to  15°  C.  [53°  to  59°  F.]  the  production  of  carbonic  acid 
is  so  rapid  that  the  bubbles  of  this  gas  carry  yeast  cells  with 
them  to  the  surface  of  the  fermenting  liquid.  The  beer 
produced  in  this  way  is  called  high  fermentation  beer  \ 
the  flavour  of  such  beer  is  not  cared  for  [in  Germany], 
[English  beer  is  generally  made  by  high  fermentation,  the 
fermentative  process  being  started  at  about  60°  F.  and  carried 
up  to  70°  F.  or  more.] 

In  Bavarian  breweries  fermentation  is  carried  on  at  from 
6°  to  8°  C.  [43°  to  46^°  F.]  ;  the  process  goes  on  very  slowly, 
and,  as  bubbles  of  carbonic  acid  form  very  gradually  and  rise 
one  by  one  to  the  surface,  the  yeast  sinks  to  the  bottoms  of 
the  vessels.  The  product  is  called  loiv  fermentation  beer ;  it 
keeps  well,  and  its  flavour  is  so  excellent  that  it  is  sent  all 
over  the  world,  and  wins  golden  opinions  everywhere.  But 
to  make  beer  drinkable  it  must  be  charged  with  carbonic 
acid  gas,  else  it  is  flat  and  insipid.  In  order  to  charge  it 


102  CHEMISTRY  IN   DAILY  LIFE 

with  the  required  quantity  of  carbonic  acid  the  fermented 
liquor  is  placed  in  barrels,  where  a  very  slow  but  continuous 
secondary  fermentation  proceeds.  The  bungs  are  placed  in 
these  barrels  a  short  time  before  the  beer  is  to  be  drunk, 
and  the  carbonic  acid,  which  continues  to  be  produced  but 
cannot  now  escape,  gradually  accumulates  in  the  beer.  The 
amount  of  carbonic  acid  produced  in  this  final  process  does 
not  exceed  about  two-tenths  of  a  per  cent. 

The  following  analyses  show  the  quantities  of  the  more 
important  constituents  in  those  beers  which  are  in  most 
demand  ;  the  numbers  given  are  the  mean  results  of  many 
analyses  : 

Water.      Carbonic      Alcohol      Sugar.        Ash. 
acid.       percentage 
by  weight. 

Draught  or  winter  beer  ...  91*81  0*228  3*206  0*442      0*20 

Lager,  or  summer  beer    ...  90*71  0*218  3*679  0*872      0*223 

Pale  beer  ( Weissbier}      ...  91*64  0*279  2*510  0*163 

Porter         87*10  0*155  5'35o  1*340      0*419 

[Burton  ale 79*6  5*90 

Scotch  ale 80*45  8'5°1 

We  must  now  consider  spirits  and  the  liquors  prepared 
from  spirits. 

Although  the  intoxicating  effect  of  wine  was  known  very 
long  ago,  yet  it  was  not  till  the  eighth  century  that  the 
intoxicating  principle  was  separated  from  wine  ;  the  separa- 
tion was  effected  by  the  Arabians  after  they  had  discovered 
the  process  of  distillation.* 

*  To  conduct  a  distillation  seems  to  us  a  very  simple  process  ;  yet  in 
the  days  of  antiquity,  although  people  were  much  interested  in  nature, 
this  method  of  separating  a  volatile  liquid  from  a  less  volatile  or  a  non- 
volatile substance  was  never  employed.  The  ancients  were  more  inclined 
towards  that  kind  of  natural  philosophy  which  expected  to  answer  all 
questions  by  speculative  thought  rather  than  to  the  genuine  scientific 
investigation  of  nature  by  means  of  experiment. 

It  was  known  in  ancient  days  that  new  and  useful  compounds  could  be 
obtained  from  various  substances  by  what  we  should  to-day  call  distilla- 


ALCOHOL  103 

When  wine  is  distilled  a  clear,  colourless,  agreeably  smell- 
ing liquid  passes  over,  the  most  striking  property  of  which 
liquid  is  its  combustibility.  This  distillate  was  named  alcohol 
by  the  Arabians.  As  this  liquid  seemed  to  be  the  spirit,  or 
essence,  of  the  wine  it  was  called  at  a  later  time  spiritus  vini. 
The  residue,  with  which  nothing  could  be  done,  was  called 
phlegm  ;  hence  Schiller's  saying,  "  Zum  Teufel  ist  der  Spiritu s, 
das  Phlegina  ist  geblieben" 

As  we  are  dealing  at  present  with  fermented  liquors  we 
will  convince  ourselves  that  there  is  a  substance  in  beer,  as 
well  as  in  wine,  which  can  be  volatilised  by  boiling,  and  is 
combustible.  Experiments  have  proved  that  the  substance 
obtained  in  this  way  from  beer  is  the  same  as  that  got  from 
wine — that,  indeed,  it  is  alcohol. 

We  pour  the  contents  of  a  bottle  of  beer  into  a  flask,  into 
which  we  then  fit  a  cork  carrying  a  glass  tube  about  a  metre 

tions.  For  instance,  Pliny  tells  that  an  oil  can  be  obtained  from 
turpentine,  which  is  a  resin  that  exudes  from  many  trees  when  their  bark 
is  cut,  by  boiling  the  turpentine  with  water  in  vessels  over  which  woollen 
cloths  are  suspended,  and  then  pressing  these  cloths  ;  and  uses  for  this 
oil  must  have  been  known,  as  it  was  prepared  in  considerable  quantities. 
But  no  one  hit  on  the  idea  of  distilling  turpentine  resin  in  order  to 
obtain  an  oil  (what  we  now  call  turpentine  oil),  and  the  exceedingly 
incomplete  method  of  getting  the  oil  described  by  Pliny  remained 
in  use. 

It  may  not  be  without  interest  to  mention  that  camphor  is  obtained 
to-day  by  the  inhabitants  of  the  island  of  Formosa  by  a  method  the  same 
as  that  described  by  Pliny  two  thousand  years  ago  for  making  an  oil 
from  turpentine  resin.  The  Formosans  boil  the  wood  of  the  camphor 
tree  with  water  in  vessels  over  which  they  place  deep  lids  filled  inside 
with  brushwood.  The  camphor  is  volatilised  with  the  steam  (some  of 
which  of  course  escapes)  and  then,  by  reason  of  the  partial  cooling, 
solidifies  on  the  brushwood  in  little  pellets  ;  the  yield  of  camphor  is  equal 
to  about  3  per  cent,  of  the  quantity  of  wood  used.  The  purification  of 
camphor  by  sublimation,  whereby  it  assumes  the  appearance  that  is 
familiar  to  us,  is  conducted  in  Europe. 


IO4 


CHEMISTRY   IN   DAILY   LIFE 


and  a  half  [almost  5  feet]  long  (see  fig.  17).  We  now  cause 
the  beer  to  boil  freely,  and  at  the  same  time  we  bring  a 
lighted  taper  to  the  opening  of  the  glass 
tube  ;  the  alcohol  vapour  that  is  rising 
from  the  tube  takes  fire  and  burns  with 
a  long  flame.  The  flame  soon  goes  out, 
as  there  is  but  a  small  quantity  of 
alcohol  in  a  bottle  of  beer  ;  nevertheless 
we  have  in  this  way,  so  to  say,  directly 
burned  out  the  alcohol  from  the  beer. 

A  great  deal  of  spirit  is  distilled  at 
the  present  time  from  wine  ;  this  spirit 
once  sufficed  for  the  total  requirements 
of  the  world,  but  to-day  it  is  used  for 
making  brandy.  Beer,  however,  has  never 
been  used  as  a  source  of  spirit,  because 
a  method  of  obtaining  spirit  from  grains 
was  discovered  long  ago,  and  this  method 
is  much  less  complicated  than  the  brew- 
ing of  beer. 

The  process  seems  to  have  been 
invented  in  South  Germany  about  the 
year  1500.  The  main  points  in  the 
manufacture  are  as  follow. 

The  raw  material  is  rye,  or  a  mixture 
of  barley  and  rye.  [Maize,  rice,  oats, 
sugar,  and  molasses  are  also  made  use 
of  in  this  country  ;  but  barley  is  the 
substance  generally  employed.]  The 
earlier  stages  in  the  manufacture  are 
similar  to  the  earlier  stages  of  brewing  ; 
moistened  barley  is  allowed  to  germinate;  but  the  malt 


Fig.  17. 


YEAST  105 

thus   formed    is    not    generally   dried — as   is   done   in   beer 
brewing — but  is  subjected  to  further  treatment. 

The  diastase  of  the  malt,  which  brings  about  the  change  of 
starch  into  sugar  and  dextrin,  is  able  to  effect  this  change  in 
a  much  larger  quantity  of  starch  than  that  which  is  contained 
in  the  malt.  If  the  mashed  rye  [or  barley],  which  has  been 
boiled  with  water  in  order  to  set  free  the  starch  granules,  is 
covered  with  water  at  about  60°  C.  [140°  F.],  and  malt  is  then 
added,  all  the  starch  in  the  grain  as  well  as  that  in  the  malt 
can  be  converted  into  sugar.  The  sweet  liquid  thus  produced 
is  then  subjected  to  fermentation  by  means  of  yeast  which  the 
distiller  prepares  for  his  own  use. 

The  preparation  of  yeast  is  closely  associated  with  the 
production  of  what  is  now  generally  called  pressed  or  dry 
yeast  (Presshefe)  [German  yeast],  which  is  so  convenient  that 
it  is  almost  always  employed  nowadays  for  bringing  about 
fermentations.  This  yeast  is  used  by  the  bakers  of  wheaten 
bread  (see  p.  86)  ;  and  also  when  bread  is  baked  at  home. 
The  procedure  used  to  be  as  follows.  The  fermentation 
whereby  the  yeast  for  use  in  making  spirits  was  to  be  produced 
was  carried  on  energetically,  and  was  of  the  kind  called  high 
fermentation  [that  is,  the  yeast  is  carried  to  the  top  of  the 
fermenting  liquid  by  the  stream  of  carbonic  acid  which  is 
freely  produced].  For  this  purpose  a  wort  was  prepared  from 
one  part  malted  barley  and  five  parts  crushed  rye  ;  yeast  was 
added,  and  the  temperature  was  kept  up  to  nearly  40°  C. 
[104°  F.],  which  is  much  higher  than  that  whereat  fermentation 
is  usually  conducted.  After  1895,  it  became  customary  to 
lead  air  into  the  fermenting  wort,  as  that  was  found  to 
promote  growth  of  yeast  and  to  increase  the  yield.  The 
fermentation  was  conducted  at  a  high  temperature  because 
that  was  required  to  produce  lactic  acid  in  quantity  sufficient 


106  CHEMISTRY  IN   DAILY  LIFE 

to  keep  the  fermentation  going.  Since  1900,  the  process  has 
been  conducted  by  adding  a  little  sulphuric  acid,  in  place  of 
depending  on  lactic  acid  produced  in  the  operation.  This 
modification  greatly  quickens  the  process,  and  increases  the 
yield  of  yeast.  The  astonishing  advance  made  in  this  part  of 
the  fermentation  industry  is  shown  by  the  following  data. 
About  14  to  15  per  cent,  yeast,  and  about  30  to  32  per  cent, 
spirits,  was  obtained  from  100  parts  of  grain  ;  after  a  time  the 
percentage  of  yeast  was  increased  to  about  20  per  cent,  and 
that  of  spirits  decreased  to  about  20  per  cent.  Since  the  use 
of  sulphuric  acid  became  common,  about  40  per  cent,  yeast  is 
obtained,  with  only  about  12  per  cent,  spirits. 

In  order  to  prepare  dry  yeast,  a  workman  skims  off  the 
masses  of  yeast  from  the  surface  of  the  liquid,  and  places  them 
in  a  hair  sieve  floating  on  water  in  a  barrel.  The  yeast  cells 
pass  through  the  sieve  and  gradually  settle  down  to  the 
bottom  of  the  barrel,  while  all  the  coarser  particles  of  solid 
matter  remain  in  the  sieve.  When  the  yeast  has  settled  the 
water  in  the  barrel  is  drawn  off,  fresh  water  is  added  and  is 
shaken  up  with  the  yeast,  which  is  then  allowed  to  settle 
again,  and  these  processes  are  repeated  several  times.  When 
the  last  lot  of  water  has  been  drawn  off  the  yeast  is  left  as  a 
fine  mud-like  deposit,  which  is  dried  by  pressure. 

The  sweet  liquid  prepared  in  the  way  already  described 
from  malt  and  mashed  rye  [or  barley]  is  caused  to  ferment 
quickly,  for  the  purpose  of  making  spirits,  by  adding  active 
yeast  to  it.  The  special  method  used  in  the  fermentation  is 
closely  connected  with  the  way  in  which  the  excise  duties  on 
spirits  are  levied.  And  the  method  which  is  most  in  harmony 
with  the  excise  arrangements,  which  arrangements  differ  very 
much  in  different  countries,  is  found  to  pay  the  best.  The 
fermented  liquid  is  finally  distilled,  and  the  distillate,  which, 
like  the  spirit  from  wine,  has  an  agreeable  odour  and  flavour, 


SPIRITS  FROM   POTATOES  IO/ 

is  used  for  making  various  kinds  of  liquors.  [Whisky  is  made 
by  re-distilling,  and  so  concentrating,  this  distillate  ;  it  con- 
tains from  60  to  78  per  cent,  alcohol  by  weight.]  The  residue 
left  in  the  distilling  vessels  is  known  as  vinasse ;  we  shall 
speak  of  this  immediately. 

Spirits  have  been  obtained  from  potatoes  since  about  the 
year  1820.  Although  there  is  nothing  of  a  spirituous  nature 
in  potatoes,  yet  when  we  remember  what  large  quantities  of 
starch  they  contain  we  at  once  see  that  an  alcoholic  liquid 
can  be  obtained  from  them  by  first  converting  their  starch 
into  sugar. 

Indeed,  a  glance  at  the  numbers  which  represent  the 
average  compositions  of  growing  potatoes  and  rye  shows  that 
much  more  spirit  can  be  obtained  from  a  given  piece  of  land  by 
raising  potatoes  than  by  growing  rye  thereon.  About  1,600 
kilograms  of  rye  are  harvested,  on  an  average,  from  a  hectare 
of  land  ;  and  as  rye  contains  about  65  per  cent,  of  starch  this 
is  equivalent  to  about  1,040  kilograms  of  starch.  But  about 
16,000  kilograms  of  potatoes  are  obtained,  on  an  average, 
from  a  hectare  of  land  ;  and,  taking  the  starch  in  potatoes  as 
not  more  than  18  per  cent,  on  an  average,  this  corresponds  to 
2,880  kilograms  of  starch.  [One  acre  yields  I2j  cwts.  rye, 
equal  to  8J-  cwts.  starch;  and  one  acre  yields  125  cwts. 
potatoes,  equal  to  22|  cwts.  starch.] 

When  the  process  of  manufacturing  spirits  from  potatoes 
had  once  taken  root  it  flourished  exceedingly,  especially  in  the 
Eastern  Elbe  provinces  of  Germany  ;  and  these  provinces 
were  much  enriched  for  many  years  by  this  industry. 

We  know  that  the  starch  granules  of  potatoes  are  enclosed 
in  a  husk  (see  p.  84).  The  custom  in  the  manufacture  of 
spirits  was  to  set  the  granules  free  from  the  husks  by  boiling  ; 
but  the  experience  of  years  has  shown  that  all  the  granules 


108  CHEMISTRY   IN   DAILY   LIFE 

cannot  be  so  thoroughly  deprived  of  their  husks  by  this 
simple  plan  as  to  enable  the  diastase  to  convert  them  com- 
pletely into  sugar.  That  this  transformation  into  sugar  may 
be  completed,  which  must  be  done  if  the  maximum  yield  of 
spirit  is  to  be  obtained,  it  is  now  customary  to  boil  the 
potatoes  in  closed  vessels,  and  not,  as  formerly  was  done,  in 
open  vessels. 

It  is  more  difficult  to  cause  water  to  boil  in  a  closed  than  in 
an  open  vessel.  Just  as  water  boils  much  under  100°  C. 
[212°  F.]  in  a  vessel  from  which  the  air  has  been  removed 
(see  p.  75),  so  the  boiling-point  is  raised  above  212°  F.  in  a 
closed  vessel,  because  of  the  pressure  on  the  surface  of  the 
water  of  the  water- vapour  which  cannot  escape  from  the 
vessel.  When  the  pressure  on  water  is  increased  to  four 
times  that  of  the  ordinary  pressure,  or,  as  is  generally  said,  to 
four  atmospheres,  the  water  does  not  boil  until  it  attains  the 
temperature  of  about  1 50°  C.  [302°  F.]  ;  and  the  custom  is  to 
heat  water  with  the  potatoes  under  this  pressure,  and  there- 
fore to  this  temperature,  in  vessels  called  steamers.  When 
the  water  in  the  steamers  is  boiled  it  of  course  attains  the 
temperature  of  1 50°  C.  [302°  F.] ;  when  this  temperature  is 
reached  a  valve  in  the  bottom  of  the  vessel  is  opened  suddenly, 
and  the  contents  are  forced  out  into  barrels  placed  ready  to 
receive  them.  The  excess  of  pressure  is  at  once  removed, 
and  the  water,  some  of  which  is  enclosed  in  the  cells  of  the 
potatoes,  and  which  is  too  hot  by  90°  F.,  suddenly  becomes 
vapour,  for  the  formation  of  which  the  whole  of  the  excess  of 
heat  must  be  employed.  The  result  is  that  all  the  cells  are 
thoroughly  broken  up,  and  the  starch  granules  are  set  free  so 
completely  that  they  can  all  be  acted  on  by  the  diastase  and 
converted  into  sugar. 

The  next  process  consists  in  adding  barley  malt  to  the 
potatoes,  mashed  with  water,  and  so  converting  the  starch 


SPIRITS   FROM   POTATOES  IOp 

into  sugar.  This  sweet  liquid  is  then  fermented  by  yeast  in 
the  way  we  have  already  described.  Finally  the  liquid  is 
distilled,  and  the  spirit  is  thus  obtained. 

The  residue  from  the  preparation  of  potato  spirit,  as  well  as 
that  from  the  manufacture  of  spirit  from  grain,  is  known  as 
vinasse.  This  substance  is  an  excellent  food  for  cattle  ;  for  a 
little  consideration  will  show  that,  as  only  the  starch  is 
removed  from  the  grain  or  the  potatoes,  the  nitrogenous 
substances — that  is,  the  albuminoids — remain  as  such  in  the 
residue.  Now  we  know  that  these  substances  are  exceed- 
ingly nourishing ;  hence  the  distilling  of  spirits  makes  it 
possible  for  the  agriculturist  to  maintain  a  greater  head  of 
cattle  than  he  could  support  on  the  same  quantity  of  land 
without  the  aid  of  this  manufacture,  and  in  this  way  spirit- 
making  furthers  agriculture. 

The  spirit  obtained  in  the  potato  distilleries  is,  however, 
very  different  from  that  produced  from  wine  or  grain.  The 
latter  spirit  can  be  used  directly  for  making  whisky,  brandy, 
etc.,  as  it  has  an  agreeable  flavour  and  odour.  But  the  raw 
potato  spirit  must  be  purified  in  spirit  refineries  before  it  can 
be  used  as  a  liquor.  For  when  potato  wort  is  fermented 
there  is  produced,  besides  ordinary  alcohol  and  carbonic 
acid,  a  series  of  other  compounds,  which,  although  they 
are  classed  by  chemists  among  the  alcohols,  nevertheless 
act  on  the  human  organism  in  a  way  very  different  from 
that  of  ordinary  alcohol.  These  substances  are  chiefly  amyl 
alcohols,  to  give  them  their  chemical  name,  and  these  alcohols, 
which  are  all  classed  together  in  ordinary  language  under  the 
name  of  fusel  oil,  act  as  poisons ;  the  smell  of  them  is 
oppressive  and  causes  choking.  They  must  therefore  be 
removed  from  the  raw  spirit  ;  this  removal  is  effected  on  the 
large  scale  in  the  following  way. 


IIO  CHEMISTRY  IN   DAILY  LIFE 

The  raw  potato  spirit  usually  contains  about  80  per  cent, 
alcohol  and  20  per  cent,  water,  together  with  fusel  oil  dis- 
solved in  these.  If  water  is  added  until  there  is  about  50  per 
cent,  of  alcohol  in  the  liquid,  the  fusel  oil,  being  no  longer 
easily  soluble  in  this  diluted  spirit,  separates  in  very  fine 
drops  which  cause  the  liquid  to  become  turbid.  The  liquid 
diluted  to  50  per  cent,  of  alcohol  is  filtered  through  wood 
charcoal ;  the  fine  drops  of  fusel  oil  adhere  to  the  charcoal, 
and  are  thus  removed  from  the  liquid.  At  the  same  time  the 
charcoal  removes  the  colouring  matter  and  the  substances 
which  impart  an  objectionable  odour  to  the  alcoholic  liquid 
(cf.  p.  42). 

The  filtered  alcoholic  liquid  is  now  brought  to  a  percentage 
of  96  per  cent,  alcohol,  by  a  method  based  on  the  following 
principle. 

We  remember  that  we  found  it  possible  to  burn  out  the 
alcohol  from  beer,  after  a  long  glass  tube  had  been  attached 
to  the  flask  wherein  the  beer  was  boiling.  No  explanation 
was  given  at  the  time  of  the  reason  for  using  so  long  a  tube, 
because  to  stop  then  and  explain  would  have  taken  attention 
away  from  the  main  point  of  the  experiment ;  the  tube  was 
made  long  in  order  that  the  alcohol  vapour  might  be  com- 
pletely separated  from  the  water  vapour.  Had  we  attempted 
to  set  fire  to  the  alcohol  vapour  at  the  mouth  of  the  flask  we 
should  have  failed,  because  the  vapour  of  alcohol  was  mixed 
with  so  much  water  vapour  at  that  point  that  the  mixed 
vapour  would  not  have  ignited.  But  a  separation  of  the 
vapours  was  effected  by  causing  them  to  pass  through  the 
long  tube,  inasmuch  as  the  heavier  water  vapour  fell  behind 
the  comparatively  light  vapour  of  alcohol,  and  the  latter 
issued  from  the  upper  opening  of  the  tube  mixed  with  so 
little  water  vapour  that  the  alcohol  took  fire  when  a  light  was 
brought  to  the  end  of  the  tube.  Spirit  is  made  as  con- 


SPIRITS   FROM   WOOD  III 

centrated  as  possible,  by  the  use  of  this  principle,  in  order  to 
save  cost  of  carriage  ;  this  is  done  by  fitting  to  the  dis- 
tillation vessel  a  long  cylindrical  apparatus  adapted  internally 
for  the  purpose  of  separating  the  vapours  of  alcohol  and 
water.  Spirit  obtained  in  this  way  never  contains  more  than 
96  per  cent,  of  alcohol,  as  the  remaining  4  per  cent,  of  water 
is  chemically  combined  with  the  alcohol. 

It  is  only  within  the  last  hundred  years  that  alcohol  of 
100  per  cent.,  that  is,  quite  free  from  water,  has  been  pre- 
pared. This  is  done  by  adding  burnt  lime  to  the  96  per  cent 
spirit ;  the  burnt  lime  is  slaked  by  the  water  in  the  spirit, 
that  is,  the  water  enters  into  chemical  union  with  the  lime,  so 
that  when  distillation'  is  again  carried  out  the  water  is 
retained  by  the  lime,  and  absolute  alcohol^  that  is,  alcohol  of 
100  per  cent.,  passes  over. 

Since  1904  the  preparation  of  spirits  from  wood  has  be- 
come an  important  industry.  When  wood  is  boiled  with 
sulphurous  acid,  a  liquid  is  obtained  which  can  be  fermented 
by  yeast.  The  manufacture  of  spirits  by  this  process  was 
greatly  developed  in  America  ;  as  much  as  8  litres  of  spirits 
have  been  obtained  from  100  kilograms  of  wood  shavings 
[nearly  2  gallons  from  2  cwts.].  But  this  method  has  been 
overshadowed  by  the  discovery,  made  in  1908,  that  spirits 
can  be  prepared  from  the  residue  obtained  in  making  cellu- 
lose from  wood,  that  is,  from  material  which  costs  nothing. 
We  know  that  sugar  is  prepared  from  raw  sugar,  but  that 
sugar  already  exists  in  certain  plants.  The  sap  of  the  maple 
tree  is  rich  in  sugar.  About  9,000,000  kilograms  [about 
9,000  tons]  of  maple  sugar  are  made  yearly  in  Canada.  This 
sugar  has  an  agreeably  aromatic,  somewhat  bitter  taste.  It 
is  not  then  to  be  wondered  at  that  sugar  should  be  found 
in  fir  and  pine  trees.  When  the  wood  of  fir  or  pine  trees 
is  boiled  with  acid  sulphite  of  lime  for  the  preparation  of 


112  CHEMISTRY  IN   DAILY  LIFE 

cellulose — we  shall  learn  more  of  this  process  in  Lecture 
VIII. — sugar  goes  into  solution  in  the  liquor.  When  this 
liquor  is  treated  with  yeast,  under  proper  conditions,  the 
sugar  in  it  ferments  ;  100  kilograms  of  wood  yield  about 
3  litres  spirits  [about  f  gallon  of  spirit  from  2  cwts.  of  wood]. 
Strange  to  say,  this  spirit  is  denaturalised  (see  forward), 
inasmuch  as  a  substance  (called  wood-spirit)  is  present  in 
the  liquor  which  distils  over  with  the  spirit,  and  renders  it 
undrinkable. 

This  is  the  place  to  mention  methylated  or  denaturalised 
spirit.  As  alcohol  and  alcoholic  drinks  are  used  as  beverages 
they  are  favourite  subjects  for  taxation  in  all  countries.  But 
the  manufacture  of  spirits  is  advantageous  to  the  farmer, 
not  only  by  giving  him  spirit  itself,  but  also  by  providing 
him  with  a  valuable  fodder  for  cattle  in  the  form  of  the 
residues  from  the  processes  of  distillation.  It  cannot  be 
to  the  interest  of  the  State  to  place  hindrances  in  the  way 
of  a  manufacture  which  is  so  advantageous  to  the  farmer, 
provided  the  State  can  arrange  the  tax  so  that  it  shall  fall 
upon  the  spirit  consumed  as  a  beverage,  and  place  an  obstacle 
in  the  way  of  excessive  drinking.  Why,  for  instance,  should 
the  State  tax  spirit  to  be  used  for  heating  purposes?  It 
does  not  tax  wood  or  coal. 

Some  means  must  be  found  for  insuring  that  spirit  meant 
for  heating  purposes,  or  for  use  in  various  industries,  cannot 
be  consumed  secretly  as  a  drink.  Spirit  must  be  robbed 
of  those  properties  for  which  people  drink  it ;  its  nature  must 
be  changed. 

This  purpose  is  effected  by  adding  substances  which  do 
not  alter  the  combustibility,  etc.,  of  the  spirit,  but  by 
their  odour  and  taste  make  the  spirit  undrinkable,  and 
cannot  be  removed  except  by  those  who  have  considerable 


METHYLATED  SPIRIT— LIQUEURS  113 

chemical  knowledge  and  have  also  suitable  apparatus  at  their 
command.  * 

[Methyl  alcohol,  or,  as  it  is  more  commonly  called,  wood 
naphtha,  is  the  substance  used  in  Great  Britain  for  this 
purpose.  In  1855  the  Board  of  Inland  Revenue  sanctioned 
the  employment  in  various  industries  of  a  mixture  of  nine 
parts  ethylic  alcohol  (spirits  of  wine)  and  one  part  methylic 
alcohol,  and  they  agreed  to  allow  the  use  of  this  methylated 
spirit  duty-free  under  certain  restrictions.] 

The  preparation  of  pure  spirit  for  making  spirituous 
liquors  is  not  to-day  a  very  difficult  undertaking.  The  shops 
where  these  liquors  are  sold  are  generally  still  called  dis- 
tilleries [in  Germany].  This  name  is  a  survival  from  the  time 
when  the  proprietors  of  the  shops  themselves  carried  on  the 
preparation  of  distilled  liquors  on  a  small  scale,  whereas 
nowadays  the  industry  is  conducted  by  large  manufacturers. 

Liqueurs  are  now  made,  very  conveniently,  by  diluting  the 
spirit  obtained  from  the  large  manufacturers  till  it  acquires 
the  proper  taste,  and  then  adding  sugar,  and  one  or  more  of 
those  fruit  essences  which  are  extracted  from  various  fruits 

*The  substances  allowed  by  the  law  to  be  used  for  this  purpose  [in 
Germany]  are  what  are  called  pyridine  bases.  We  have  already  learnt 
that  tar  is  produced  in  gas  making,  besides  ammonia,  which  is  a  com- 
pound of  nitrogen  and  hydrogen.  The  tar  contains  certain  nitrogenous 
substances  which  can  be  defined  chemically  as  derivatives  of  ammonia, 
and  which,  like  ammonia,  have  a  very  marked  odour ;  some  of  them 
indeed  have  an  exceedingly  disagreeable  odour.  Among  the  products 
of  the  distillation  of  gas-tar,  a  process  we  shall  have  to  consider 
hereafter,  are  those  pyridine  bases  that  are  used  for  mixing  with 
spirit  for  the  purpose  already  indicated.  As  their  name  implies,  these 
substances  are  capable  of  uniting  with  acids  to  form  salts  (see  p.  49). 

[I  have  put  this  part  of  the  text  in  a  footnote,  and  have  replaced 
it  by  the   sentences  in   a  square   bracket,  because  of  the  differences 
between  the  German  and  the  English  methods  for  making   spirit   un- 
drinkable.— TR.] 
8 


114  CHEMISTRY  IN   DAILY  LIFE 

and  are  sent  into  the  market  by  the  manufacturer.  It  is 
possible  to  prepare  such  fruit  ethers  by  purely  chemical 
methods,  without  using  fruits  at  all ;  and  those  that  are 
prepared  in  this  way  are  more  and  more  driving  out  of 
the  market  the  essences  obtained  from  the  fruits  themselves. 

Many  liqueurs  are  made  by  soaking  the  flowers  of  plants, 
for  it  is  chiefly  these  that  are  used,  for  a  long  time  in  spirit, 
and  then  drawing  off  the  liquor  which  has  acquired  the  odour 
of  the  flowers  and  also  a  peculiar  flavour. 

Brandy,  arrac,  and  rum  are  not,  however,  prepared  in  this 
way.  They  are  made  by  the  direct  distillation  of  fermented 
liquids ;  and  each  owes  its  peculiar  flavour  to  certain  sub- 
stances which  volatilise  and  condense  in  the  process  of 
distillation.*  Brandy  is  distilled  from  wine ;  the  colour 
is  derived  from  the  vessels  of  oak  wood  wherein  it  is 
stored.  Arrac  is  made  in  India,  chiefly  by  distilling  fer- 
mented rice.  The  preparation  of  a  spirituous  liquor  from 
rice  is  similar  to  the  process  we  are  accustomed  to  use  in 
preparing  corn  spirit.  Rum  is  manufactured  in  the  West 
Indies  from  fermented  sugar  molasses  (see  p.  76). 

As  these  three  liquors  are  free  from  sugar,  as  must  be  the 
case  from  the  methods  of  their  preparation,  they  may  be  used 
without  harm  by  patients  suffering  from  diabetes,  by  whom 
liqueurs  must  be  avoided. 

The  following  analyses  show  the  quantities  of  the  most  im- 
portant ingredients  in  some  of  the  spirituous  liquors  com- 
monly consumed  : 

Alcohol.  Sugar. 

Brandy     53*82  per  cent,  by  volume 

Arrac        6074        „  „  — 

Rum         77-62 

Kiimmel 33'9O        >,  »  31*18  per  cent. 

Benedictine        ...  46*20        „  „  32-57    „     „ 

*  These  substances  may  be  called  raw  spirit  with  a  very  agreeable 
flavour. 


ALCOHOL  AS  A  FOOD  115 

Before  leaving  this  part  of  our  subject  let  us  examine  the 
question,  which  we  have  hitherto  passed  over,  as  to  how  far 
alcohol  can  be  said  to  possess  any  value  as  a  food.  In  what 
has  been  said  hitherto  we  have  followed  the  example  of  all 
the  standard  authors  in  regarding  this  value  as  non-existent 
At  the  same  time  we  must  say  that,  if  starch  and  sugar  are 
foods  because  the  carbon  which  they  contain  is  finally  burnt 
in  the  body  to  carbonic  acid,  then  alcohol,  which  is  a 
substance  intermediate  between  sugar  (or  starch)  and  the  final 
product  of  the  decomposition  of  sugar — namely,  carbonic  acid — 
will  also  be  wholly  burnt,  in  the  long  run,  in  the  body.  Indeed, 
as  the  composition  of  alcohol  is  simpler  than  that  of  the  fats 
in  the  body,  which  fats  are  eventually  burnt  in  the  organism, 
alcohol  ought  to  be  more  easily  oxidised  than  these  fats,  and 
therefore  the  use  of  alcohol  should  lead  to  some  saving  in  the 
consumption  of  these  substances.  Nevertheless  many  experi- 
ments have  shown  that  the  significance  of  alcohol  as  a  source 
of  nourishment  for  people  in  good  health  is  extremely  small. 

On  the  other  hand,  experience  shows  that  matters  may  be 
very  different  in  cases  of  illness.  It  is  apparent  to  every  one 
that  the  loss  of  energy  from  which  sick  people  suffer,  who 
cannot  consume  the  ordinary  kinds  of  food,  may  often  be 
relieved  by  the  use  of  wine  or  champagne  which  they 
will  take  with  pleasure.  This  can  only  be  explained  by 
supposing  that,  although  fats  and  albuminoids  are  burnt  with 
difficulty  in  the  bodies  of  those  who  are  weakened  by  illness, 
nevertheless  alcohol,  which  is  more  easily  oxidised  than  these 
two  substances,  can  be  oxidised  even  in  their  weak  condition 
without  too  much  difficulty,  and  can  in  this  way  supply  the 
heat  and  the  vital  energy  which  are  required.* 

*  I  have  omitted  a  few  paragraphs  wherein  the  author  sets  forth 
his  opinion  regarding  the  use  of  alcohol  and  its  effects  on  the  human 
organism.— TR. 


LECTURE   VI 

Wine  vinegar — Wood  vinegar — Glacial  acetic  acid — Wood  spirit — 
Acetone — Gunpowder — Greek  fire — Fulminating  mercury — Gun- 
cotton — Dynamite — Collodion — Blasting  gelatin — Cordite — Chlorate 
explosives — Wool — Cotton — Silk — Artificial  wool  [Shoddy] — Carbon- 
ising— Mercerised  cotton — Artificial  silk. 

WE  begin  to-day  with  vinegar. 

Experience  shows  that  wine  and  beer,  which  are  alcoholic 
liquids,  become  sour  when  they  are  exposed  to  the  air 
for  some  time.  These  liquids  lose  their  intoxicating  properties, 
and  become  so  sour  that  they  are  undrinkable  except  when 
mixed  with  other  substances.  The  new  liquids,  however,  are 
used  as  adjuncts  to  food,  to  which  they  impart  an  agreeably 
sharp  flavour. 

When  an  alcoholic  liquid  becomes  sour  the  alcohol  in  it  is 
changed  to  acetic  acid,  and  the  liquid  thus  produced  is  called 
vinegar. 

We  have  learnt  that  the  juice  of  grapes  very  easily 
changes  into  wine.  The  transformation  of  wine  into  what 
is  called  wine  vinegar  takes  place  almost  as  easily,  and 
for  this  reason  wine  vinegar  has  been  known  since  very  early 
times. 

The  production  of  acetic  acid  from  alcohol  consists  in  an 
oxidation  of  the  latter  substance  ;  this  addition  of  oxygen, 
and  therefore  the  passage  from  alcohol  to  acetic  acid,  is  easily 
carried  out  in  the  laboratory.  But  the  change  is  effected  by 

116 


VINEGAR  117 

atmospheric  oxygen  only  in  the  presence  of  a  certain  mould, 
to  which  the  name  Mycoderma  aceti  is  given.  This  mould  is 
found  everywhere  in  the  air ;  it  is  active  in  liquids  which 
already  contain  vinegar. 

The  preparation  of  wine  vinegar  is  carried  on  nowadays  in 
the  following  manner.  Boiling  vinegar  is  poured  into  oaken 
barrels  so  as  to  soak  the  wood  thoroughly,  and  the  barrels  are 
then  filled  to  about  two-thirds  with  wine.  A  series  of  holes  is 
made  in  the  barrels  above  the  level  of  the  liquid  in  order  that 
air  may  have  free  access  to  the  surface  of  the  liquid.  The 
change  is  complete  after  about  fourteen  days.  Half  of  the 
liquid  is  drawn  off  to  be  sold  as  vinegar,  and  the  barrels 
are  filled  up  with  fresh  quantities  of  wine.  The  process 
may  go  on  for  some  years  before  it  is  necessary  to  clean  the 
barrels. 

It  is  necessary  for  the  normal  process  of  acidification  that 
the  wine  should  not  contain  more  than  about  10  per  cent, 
of  alcohol.  Stronger  wines  must  be  diluted  with  water. 

Cider,  perry,  and  beer  can  be  manipulated  in  a  similar  way. 
Vinegar  made  in  this  way  from  ordinary  beer  retains  a  bitter 
aftertaste,  derived  from  the  hops,  which  cannot  be  removed. 
For  this  reason  it  was  once  customary  to  prepare  a  beer 
without  hops,  for  the  special  purpose  of  manufacturing 
vinegar  from  it. 

As  the  process  of  making  vinegar  consists  essentially  in  the 
oxidation  of  alcohol  any  kind  of  commercial  spirit  may  be 
employed  for  the  purpose ;  and  large  quantities  of  vinegar 
are  made  to-day  from  commercial  spirits.  The  spirit  must 
be  diluted  until  it  contains  not  more  than  10  per  cent,  of 
alcohol  ;  it  is  then  treated  in  the  way  already  described  for 
making  vinegar  from  wine.  The  yield  of  vinegar  is,  however, 
much  smaller  when  spirit  is  used  than  when  wine  is  em- 
ployed ;  for  the  souring  of  spirit  is  as  difficult  as  the  souring 


Il8  CHEMISTRY  IN  DAILY  LIFE 

of  wine  is  easy.  For  this  reason  another  method  has  been 
employed  since  about  1 820  for  making  vinegar  from  spirits ; 
this  is  called  the  quick  vinegar  process. 

A  deep  wooden  vat,  provided  with  a  false  bottom,  is  filled 
up  with  shavings  of  beech  wood,  which  experience  has  shown 
to  be  the  most  suitable  wood  for  the  purpose.  The  shavings 
are  thoroughly  soaked  in  vinegar,  and  dilute  spirit  is  allowed 
to  trickle  slowly  on  to  the  shavings  from  the  top  of  the  vat. 
Many  holes  are  bored  in  the  sides  of  the  vat  in  such  a  way 
that  air  can  enter,  but  liquid  cannot  escape,  through  them. 
The  alcoholic  liquid  is  thus  spread  over  a  very  large  surface 
while  it  is  exposed  to  the  oxidising  action  of  the  air.  The 
acidified  liquid  collects  beneath  the  false  bottom  ;  it  is  drawn 
off,  and  passed  through  the  same  vat  three  or  four  times 
before  the  oxidation  is  completed. 

The  strongest  vinegar  that  can  be  obtained  by  this  method 
contains  about  10  per  cent,  of  acetic  acid.  The  following 
analytical  results  show  the  quantities  of  acetic  acid  in  various 
vinegars : 

Strongest  vinegar 10*30  per  cent,  acetic  acid. 

Wine  vinegar  5-37        „  „ 

Ordinary  white  vinegar      4*63        „  „ 

Ordinary  brown  vinegar     3*53        „,  „ 

Brown  vinegar  may  derive  its  colour  from  being  prepared 
from  beer  brewed  without  hops  or  from  red  wine  ;  but  it 
is  more  often  coloured  by  a  little  burnt  sugar  (see  p.  71). 

Vinegar  essence  can  be  bought  to-day  containing  from 
25  to  50  per  cent  acetic  acid,  from  which  ordinary  household 
vinegar  is  made  by  adding  water. 

The  essence  cannot  of  course  be  made  by  the  method 
already  described,  inasmuch  as  that  method  is  not  applic- 
able to  liquids  which  contain  more  than  10  per  cent,  of 


VINEGAR   ESSENCE  1 19 

alcohol,  and  therefore  produce  a  corresponding  percentage  of 
acetic  acid. 

The  source  of  this  vinegar  essence  is  quite  different  from 
that  of  ordinary  vinegar ;  it  is  made  by  the  dry  distillation  of 
wood.  We  have  already  dealt  in  detail  with  the  dry  distilla- 
tion of  coal  (see  gas  making,  p.  28),  the  chief  products  of 
which  are  gas,  an  aqueous  liquid  (ammonia  water),  tar  and 
coke.  Products  corresponding  with  these  are  obtained  by 
the  dry  distillation  of  wood.  But  gas  from  wood  cannot 
compete  with  coal-gas,  and  is  scarcely  used,  while  the  watery 
liquid  obtained  by  the  distillation  of  wood  is  not  basic,  like 
ammonia  water,  but  has  acid  properties.  This  liquid  con- 
tains acetic  acid,  mixed  with  a  great  many  other  substances 
which  are  used  in  ordinary  life,  just  as  the  crude  acetic  acid 
is  used  under  the  name  of  wood  vinegar.  The  residue  in  the 
retorts  is  wood  charcoal. 

Wood  spirit  is  one  of  the  liquid  products  of  the  dry 
distillation  of  wood.  The  chemical  composition  of  this 
substance  is  that  of  the  simplest  possible  alcohol.  Like 
fusel  oil,  it  is  undrinkable  ;  it  is  much  used  in  England 
for  adding  to  ordinary  alcohol  to  produce  methylated  spirit 
(see  p.  113).  Another  product  of  the  dry  distillation  of  wood 
is  a  clear,  colourless  liquid  called  acetone,  the  chemical  com- 
position of  which  is  not  so  simple  as  that  of  wood  spirit. 
This  substance  is  made  use  of  in  the  production  of  aniline 
colours ;  it  is  also  much  used  as  a  solvent,  and  in  this  rdle 
we  shall  meet  with  it  again  when  we  are  considering  the 
preparation  of  smokeless  powder.  As  but  little  acetone 
is  found  in  the  products  of  distilling  woods,  this  compound  is 
prepared  in  other  ways  also. 

But  it  is  the  acetic  acid  in  the  liquid  obtained  by  distilling 
wood  which  interests  us  most  at  present.  The  acetic  acid  in 


120  CHEMISTRY  IN   DAILY  LIFE 

this  liquid  is  coloured  brown  by  the  presence  of  tarry  matters. 
Pure  acetic  acid,  free  from  water,  is  obtained  from  this  brown 
liquid  by  a  somewhat  complicated  process  of  purification. 
Pure  acetic  acid  is  a  clear,  colourless  liquid,  with  a  very 
strong  odour  of  vinegar  ;  it  has  the  property  of  solidifying 
at  a  low  temperature  to  a  solid  very  much  resembling 
ice,  which  solid  becomes  liquid  again  at  ifC.  [62 '6°  F.]. 
Because  of  this  behaviour  pure  acetic  acid  is  commonly 
spoken  of  as  glacial  acetic  acid,  a  name  which  is  quite 
superfluous  and  has  a  flavour  of  mystery  about  it.  When 
the  acid  is  diluted  with  its  own  weight  of  water  it  is  known 
as  vinegar  essence. 

We  have  now  said  enough  about  the  relations  of  foods  and 
condiments  to  human  life  ;  and  we  shall  proceed  to  consider 
other  subjects  which  require  some  chemical  knowledge  for 
their  elucidation. 

We  have  already  made  mention  of  saltpetre  in  speaking 
of  the  use  of  soda  saltpetre  as  a  source  of  nitrogen  to  the 
agriculturist  (see  p.  50).  Potash  saltpetre,  however,  is  used 
for  a  very  different  purpose  ;  it  is  the  foundation  of  all  the 
varieties  of  gunpowder,  a  substance  which  is  now  being 
partially  supplanted  by  the  smokeless  powders  introduced 
about  the  year  1886. 

Potash  saltpetre  is  the  salt  that  is  formed  by  combining 
the  base  potash  with  nitric  acid  (see  p.  49).  Now  if  nitric 
acid  is  allowed  to  react  with  such  an  organic  substance 
as  cellulose  (regarding  which  we  shall  learn  more  when  we 
consider  the  manufacture  of  paper),  a  compound  is  formed 
by  the  nitrogroup  of  the  nitric  acid  entering  into  the 
molecule  of  the  cellulose  ;  this  nitrogroup  consists  of  an  atom 
of  nitrogen  combined  with  two  atoms  of  oxygen.  The 
compound  formed  in  this  way  is  called  nitrocellulose  ;  this 


GREEK  FIRE  121 

compound,  and  others  similar  to  it,  form  the  basis  of  the 
newer  explosives  and  also  of  smokeless  powder,  substances 
which  have  to  be  dealt  with  later. 

The  compound  of  nitrogen  and  oxygen  which  is  fixed  in 
gunpowder  in  the  form  of  saltpetre  is  also,  in  the  form  of 
the  nitrogroup,  the  explosive  ingredient  in  all  modern  smoke- 
less powders.  Notwithstanding  innumerable  attempts,  no 
better  or  equally  good  substitute  for  this  compound  has 
been  discovered. 

Neither  the  Greeks  nor  the  Romans  were  acquainted  with 
saltpetre,  nor  with  any  mixture  resembling  gunpowder. 
Saltpetre  seems  to  have  come  into  Europe  in  the  fifth 
century,  from  India  or  China,  by  way  of  Constantinople. 

The  discovery  was  made  in  the  Arsenal  at  Constantinople 
that  if  combustible  substances  were  mixed  with  saltpetre 
these  substances  could  be  burned  in  such  a  way  that  the 
burning  did  not  cease  until  the  mixture  was  entirely  con- 
sumed. We  now  know  that  this  property  of  saltpetre  is 
connected  with  the  large  quantity  of  oxygen,  47*5  per  cent., 
which  the  salt  contains.  The  saltpetre  brings  oxygen,  which 
we  know  to  be  the  most  important  element  in  processes  of 
combustion,  in  the  solid  form,  into  any  mixture  of  which 
the  saltpetre  is  an  ingredient. 

It  was  soon  found  that  the  most  suitable  mixture  for 
burning  was  one  made  of  saltpetre,  charcoal,  and  sulphur. 
The  mixture  .was  known  as  Greek  fire,  and  by  its  use 
Constantinople  was  able  to  defend  herself  for  a  long  time 
from  all  her  enemies.  The  Arabian  fleet  was  burnt  by  the 
use  of  this  substance  in  the  seventh  century,  and  at  last  the 
Arabs  abandoned  the  attempt  to  conquer  the  city.  Western 
Europe,  which  did  not  possess  this  means  of  defence,  could 
not  resist  the  Arabs,  who  crossed  into  Spain  in  711,  and  for 
many  centuries  ruled  that  country.  In  the  tenth  century 


122  CHEMISTRY  IN   DAILY  LIFE 

Constantinople  used  Greek  fire  to  drive  back  an  inroad 
made  by  Bulgarians.  This  substance,  Greek  fire,  has 
evidently  played  an  important  part  in  the  development  of 
the  nations,  and  the  discovery  of  the  modification  of  Greek 
fire  which  we  call  gunpowder  has  increased  this  influence. 
It  is  a  noteworthy  fact  that,  although  all  these  peoples  who 
fought  against  Constantinople  tried  to  discover  the  secret  of 
making  Greek  fire,  nevertheless  the  secret  was  kept  for  five 
or  six  hundred  years.  Such  a  fact  seems  to  us  to  be  almost 
inexplicable.  We  cannot  understand  how  a  discovery  of  so 
much  importance  should  have  been  made  so  long  ago,  nor 
how  the  city  that  was  in  possession  of  this  secret  should  have 
been  able  to  keep  it  almost  up  to  modern  times. 

The  earliest  writings  that  give  an  account  of  the  com- 
position of  Greek  fire  are  those  of  the  Byzantine  author 
Marcus  Graecus,  who  lived  about  the  year  1200.  A  Latin 
translation  of  a  book  by  this  author  has  come  down  to  us ; 
its  title  is  Liber  Ignium  ad  Comburendos  Hostes  (Book  of  Fires 
for  destroying  the  Enemies).  It  does  not  appear  from  this 
book  that  Marcus  Graecus  was  the  first  to  publish  to  the 
world  the  secret  of  making  Greek  fire  ;  it  rather  seems  as  if 
the  knowledge  of  the  manufacture  had  already  spread  by 
word  of  mouth,  and  that  Constantinople  could  no  longer 
claim  the  monopoly  of  the  process. 

The  book  of  Marcus  Grrecus  always  speaks  of  Greek  fire 
as  merely  a  very  combustible  mixture,  although  the  composi- 
tion of  the  mixture  described  in  the  book  is  not  very  different 
from  the  compositions  of  the  gunpowders  that  are  used  to- 
day for  military  purposes.  The  following  figures  show  this  : 

Greek  fire,  according  to      Prussian  military 
Marcus  Graecus.  gunpowder  in  1886. 

Sulphur         ii  per  cent.  10  per  cent. 

Carbon          22        „  16       „ 

Saltpetre       67       „  74       „ 


GUNPOWDER  123 

There  is  now  no  chance  of  finding  out  when  and  by  what 
means  the  discovery  was  made  that  a  most  energetic 
explosive  power  was  hidden  in  this  mixture — an  explosive 
power  which  was  indeed  greater  than  that  of  any  other 
artificially  produced  substance  then  known.  This  discovery 
was  soon  turned  to  account  for  the  purposes  of  war  ;  the  first 
metal  cannons  were  cast  at  Florence  in  1326,  and  soon  after 
this  we  find  enumerations  of  the  pieces  of  artillery  brought 
into  action  in  the  battles  and  sieges  of  the  period.  But  the 
explosive  was  not  used  in  hand  weapons  until  a  much  later 
period.  About  the  year  1 500  soldiers  who  used  guns  stood 
in  files  thirty-seven  deep  ;  the  reloading  of  the  weapons 
occupied  so  much  time  that  when  a  man  had  fired  he  passed 
to  the  rear,  and  he  was  not  ready  to  fire  again  until  the 
thirty-six  men  in  front  of  him  had  discharged  their  weapons. 
This  state  of  affairs  lasted  till  the  time  of  Frederick  the 
Great,  when  such  great  improvements  were  made  in  flintlock 
guns  that,  since  then,  the  gain  or  loss  of  battles  has  depended 
very  largely  on  the  fire  of  the  infantry. 

The  use  of  gunpowder  as  an  explosive  agent  in  mining  did 
not  begin  until  1627. 

Many  attempts  to  improve  gunpowder  have  of  course  been 
made  from  time  to  time  ;  but  the  figures  already  given  show 
that  the  changes  made  in  its  composition  have  not  been 
very  marked.  In  former  times  the  preparation  of  gunpowder 
was  a  very  simple  operation  ;  the  three  ingredients  were 
mixed  and  the  thing  was  done.  In  the  nineteenth  century, 
great  advances  were  made  in  this,  the  purely  technical  part  of 
the  manufacture.  The  method  of  mixing  the  powder  which 
is  made  in  the  largest  quantities,  that,  namely,  for  use  in 
mines,  had  been  carried  to  very  great  perfection,  and  at  the 
same  time  the  most  suitable  size  of  grains  had  been  found  out 


124  CHEMISTRY  IN   DAILY  LIFE 

long  ago.  Powder  to  be  used  in  large  cannons,  for  instance, 
was  pressed  into  the  form  of  six-sided  prism-shaped  pieces, 
several  centimetres  long.  The  pieces  of  this  prismatic  powder 
were  pierced  with  holes,  which  insured  the  simultaneous 
burning  of  the  grains  from  within  and  from  without.  Never- 
theless, this  powder  burnt  much  more  slowly  than  that  made 
in  fine  grains.  Hence  the  force  of  the  explosion  in  a  tube 
took  effect  more  slowly  when  large  grained  powder  was  used, 
and  for  this  reason  powder  of  this  kind  was  more  effective  in 
the  'modern  very  large  cannons. 

We  have  mentioned  only  one  of  the  advances,  based  on 
logical  reasoning,  that  have  been  made  in  the  preparation  of 
the  most  useful  kind  of  powder,  to  make  clear  that,  although 
gunpowder  reminds  us  of  Greek  fire  so  far  as  its  composition 
is  concerned,  yet  the  Greek  fire,  that  was  thrown  like  a  burning 
torch  at  the  enemy,  was  merely  a  plaything  compared  with 
the  modern  powder. 

The  following  figures  show  what  can  be  done  with 
prismatic  gunpowder.  A  cannon  exhibited  by  Krupp  at 
the  Chicago  exhibition,  when  charged  with  115  kilos,  [253 
Ibs.]  of  this  powder  propelled  a  shot  weighing  215  kilos. 
[473  Ibs.]  to  a  distance  of  20,226  metres  [i2j  miles];  the 
flight  of  the  shot  occupied  71  seconds,  and  the  highest 
point  attained  was  6,540  metres  [4  miles]  above  the  earth, 
while  the  height  of  Chimborazo  is  only  6,421  metres  [3*99 
miles]. 

The  great  advances  recently  made  in  chemistry  have  led  to 
a  complete  revolution  in  regard  to  gunpowder.  Very  ex- 
plosive substances  have  long  been  known  in  the  laboratory, 
but  the  extraordinary  violence  of  their  action  made  it 
impossible  to  use  them  in  guns,  because  they  would 
burst  the  gun  before  they  could  set  the  shot  in  action. 
Only  one  compound  found  an  application  in  connection 


GUNCOTTON  12$ 

with  guns,  and  that  was  fulminating  mercury,  a  substance 
which  explodes  when  struck  sharply.  It  was  used  in  per- 
cussion caps  for  starting  the  explosion  of  the  powder  in 
the  gun,  in  place  of  the  flintlock  which  had  succeeded  the 
untrustworthy  and  unsafe  tinder.  In  the  flintlock  the 
igniting  spark  was  produced  by  the  fall  of  a  piece  of  steel 
on  flint. 

When  gunpowder  explodes  a  great  deal  of  smoke  is 
produced.  The  smoke  consists  of  compounds  of  the 
potassium  contained  in  the  nitre  of  the  powder.  This  very 
stable  metallic  substance  is  changed  during  the  explosion 
into  sulphate  of  potash  and  other  similar  compounds  ;  these 
substances  are  solids,  and  they  are  broken  up  by  the 
explosion  into  a  very  fine  dust  that  floats  in  the  air  for 
a  long  time  and  forms  the  smoke  of  the  powder.  Matters 
are  quite  different  when  a  little  guncotton  is  ignited — and 
we  must  now  proceed  to  consider  this  substance  ;  the 
guncotton  burns  instantaneously  and  without  a  trace  of 
smoke. 

Why  then  should  there  be  this  great  difference  between 
the  old  and  the  new  explosive  substance?  Cotton  wool 
consists  of  cellulose,  a  compound  of  six  atoms  of  carbon,  ten 
atoms  of  hydrogen,  and  five  atoms  of  oxygen  ;  it  has 
therefore  the  same  composition  as  starch  (see  p.  67)  ;  it  is 
a  carbohydrate.  When  cotton  wool  is  treated  with  nitric 
acid,  the  action  of  which  is  increased  by  the  addition  of 
sulphuric  acid — the  mixture  of  these  acids  is  technically 
known  as  "  nitroacid" — nitrogroups  enter  into  the  cellulose 
molecule,  as  has  been  mentioned  already.  While  the  old 
powder  was  a  mixture  of  substances  prepared  as  carefully 
as  possible,  the  new  explosive  substance  is  itself  a  chemical 
compound.  The  old  powder  burnt  away ;  when  the  new 


126  CHEMISTRY  IN  DAILY  LIFE 

substance  is  used  as  an  explosive  there  ensues  an  instan- 
taneous falling  to  pieces  of  the  molecule.  While  a  kilogram 
(2^  Ibs.)  of  powder  requires  about  the  hundredth  part  of 
a  second  for  its  combustion,  about  one-fifty-thousandth  part 
of  a  second  suffices  for  the  decomposition  of  a  kilogram  of 
guncotton. 

When  guncotton  is  burnt  carbonic  acid  is  produced  from 
the  carbon  and  water  from  the  hydrogen,  and  the  necessary 
oxygen  comes  partly  from  the  cotton  wool,  but  more 
particularly  from  the  nitrogroups — for  several  nitrogroups 
enter  into  the  molecule  of  cellulose  when  guncotton  is  made. 
The  nitrogen  of  the  nitrogroups  is  given  off  as  nitrogen. 
As  we  have  seen,  the  explosion  of  this  material  produces 
gaseous  substances  only,  for  the  water  that  is  formed  is 
gaseous  at  the  high  temperature  whereat  the  burning  is  com- 
pleted. /  As  these  gases  are  colourless  they  are  of  course 
invisible  ;  guncotton  therefore  burns  without  any  smoke. 

Guncotton  was  the  first  of  the  more  recently  discovered 
explosives  that  was  found  to  be  practically  useful  ;  and  soon 
after  its  discovery,  which  was  made  in  the  year  1846,  many 
countries  laid  in  great  stocks  of  this  substance.  But  the 
stores  of  guncotton  sometimes  exploded  suddenly  without 
any  apparent  reason,  and  caused  enormous  damage.  All 
confidence  in  the  material  was  lost ;  but  after  about  thirty 
years'  labour  such  definite  knowledge  has  been  obtained 
regarding  the  conditions  of  preparation  of  a  stable  substance 
that  guncotton  can  now  be  handled  without  danger.  It 
was  also  discovered  after  a  long  time — and  this  fact  has 
proved  very  important — that  wet  guncotton  is  as  convenient 
as  the  dry  material,  or  even  more  convenient,  for  explosive 
purposes.  And  nowadays  torpedoes  charged  with  rolls  of 
moist  guncotton  which  has  been  subjected  to  enormous 
pressures  are  possessed  of  such  great  destroying  power  that 


GU  NCOTTON —DYNAMITE  1 2? 

even  the  best  defended  vessels  cannot  withstand  the  impact 
of  these  weapons. 

The  charging  of  these  torpedoes  is  perfectly  safe,  inasmuch 
as  moist  guncotton  obstinately  refuses  to  ignite  when  brought 
into  contact  with  an  ordinary  flame.  Explosion  takes 
place  only  after  burning  has  been  started  ;  and  this  fact 
is  the  essential  part  of  the  most  important  discovery  just 
mentioned. 

To  say  that  explosion  occurs  only  after  burning  has  been 
started  means  that  the  guncotton  must  receive  a  shock  which 
in  the  physical  sense  is  extremely  sharp.  Such  a  shock  is 
produced  by  the  explosion  of  fulminating  mercury,  for 
instance.  If  a  detonator  of  this  material  is  exploded  in  a 
mass  of  moist  guncotton  the  explosive  wave  causes  a  dis- 
ruption of  the  atoms  which  are  arranged  in  a  definite  way 
in  the  molecule  of  the  guncotton — or  nitrocellulose,  as  this 
substance  is  called  in  chemistry — resulting  in  the  falling  to 
pieces  of  the  molecule,  and  hence  in  the  explosion  of  the 
guncotton  whether  that  be  wet  or  dry. 

Long  before  it  had  become  possible  to  handle  guncotton 
with  perfect  safety,  another  of  the  modern  explosives  had 
come  into  favour  for  the  peaceful  purposes  of  mining,  etc. ; 
this  was  dynamite^  a  substance  the  name  of  which  is  now 
heard  everywhere  in  the  world. 

We  have  already  got  to  know  something  of  glycerin  as 
a  constituent  of  fat  (p.  19).  When  glycerin  is  mixed  with 
"  nitroacid "  (see  p.  25)  three  nitrogroups  are  taken  up  by 
the  glycerin  ;  the  product  is  therefore  very  rich  in  this  most 
powerful  constituent.  The  nitroglycerin  produced  in  this  way 
is  a  liquid,  like  the  material  from  which  it  is  made,  and  it  is 
not  very  suitable  for  use  as  an  explosive.  It  is  therefore 
mixed  with  a  sufficient  quantity  of  very  fine  sand,  called 
infusorial  earth  (Kieselguhr\  to  produce  a  solid  mass,  and 


128  CHEMISTRY  IN   DAILY  LIFE 

this  solid  is  known  as  dynamite,  a  substance  that  was 
employed  in  blasting  the  St.  Gotthard  Tunnel,  and  in  many 
other  works  of  a  like  character. 

Meanwhile  quantitative  deductions  from  the  theory  of 
projectiles  had  shown  that  much  more  efficient  results  would 
be  obtained  by  decreasing  the  diameter  of  the  projectiles  to 
be  used  in  cannons,  provided  that  a  greater  impulse  than  was 
possible  by  the  employment  of  gunpowder  could  be  given  to 
the  shots.  Thereupon  began  the  search  after  new  kinds  of 
military  powders — which  should  necessarily  be  smokeless,  for 
reasons  we  can  now  understand — on  the  lines  suggested  by 
the  properties  of  the  nitrocompounds.  The  discovery  by 
the  French  of  melinite  was  one  of  the  results  of  this  search. 
Melinite  was  prepared  by  the  action  of  "nitroacid"  on  carbolic 
acid,  a  substance  much  used  as  a  disinfectant.  The  result 
of  this  action  is  to  introduce  three  nitrogroups  into  the 
carbolic  acid,  and  so  to  iorm  picric  acid,  which  is  a  compound 
that,  like  guncotton,  can  be  exploded  when  moist  by  an 
initial  detonation.  The  methods  of  preparation  of  this 
powder  are  kept  as  a  State  secret ;  but  the  substance  has  not 
stood  the  test  of  time.  Guncotton  seems  to  have  come  out 
victorious  in  all  contests  with  this  competitor,  as  with  the 
other  competitors  in  the  domain  of  modern  smokeless 
powders.  At  any  rate  guncotton  appears  to  be  a  constituent 
of  all  these  powders,  as  far  as  one  can  find  out  considering 
that  the  methods  of  manufacture  of  smokeless  powders  are 
kept  secret  by  the  different  states. 

What  makes  guncotton  so  very  suitable  is  its  property  of 
dissolving  in  various  solvents  and  so  producing  a  liquid  that 
is  eminently  adapted  for  making  powders.  For  instance, 
the  well-known  substance  collodion  is  a  solution  of  guncotton 
in  a  mixture  of  ether  and  alcohol.  If  this  solution  is 


SMOKELESS  POWDER— BLASTING  GELATIN  129 

evaporated  a  film  remains,  which  can  be  obtained  of  any 
desired  thickness  ;  by  cutting  this  film  into  small  pieces  a 
smokeless  powder  is  produced.  The  technical  preparation 
is  not  so  easy  as  this,  but  still  it  is  carried  out  on  these 
lines. 

As  guncotton  alone  would  be  too  violently  explosive  for 
use  in  guns  it  is  customary  to  add  some  indifferent  substance 
— camphor,  for  instance,  was  used  for  a  long  time — to  a 
solution  of  guncotton  ;  and  then  to  evaporate  the  solution  ; 
in  this  way  a  solid  is  obtained,  which  may  be  regarded  as 
diluted  guncotton,  and  can  be  used  as  a  smokeless  powder, 
It  is  evident  that  a  powder  of  any  desired  strength,  and 
suitable  for  various  purposes,  can  be  obtained  by  this  method 
of  procedure. 

The  most  powerful  of  all  explosives  is  made  by  saturating 
guncotton  with  nitroglycerin  ;  this  explosive  is  used  in 
mining  operations,  but  it  cannot  be  employed  in  guns.1  Gun- 
cotton  does  not  dissolve  in  nitroglycerin,  but  it  swells  up  and 
forms  a  jelly-like  substance  which  is  known  as  blasting  gelatin. 
This  blasting  gelatin  is  the  most  energetic  explosive  we  have 
at  our  disposal :  the  strength  of  it  can  be  modified  by  using 
more  or  less  guncotton  ;  and  it  seems,  from  what  has  been 
said  already,  that  this  explosive  cannot  be  surpassed,  for  the 
energy  of  nitroglycerin  is  not  lessened  in  it  by  the  addition  of 
such  a  substance  as  sand,  as  is  the  case  in  making  dynamite, 
but  is  rather  increased  by  the  guncotton  that  is  employed  in 
the  manufacture. 

If  the  nitroglycerin  is  diluted  with  acetone  (see  p.  119) 
before  the  guncotton  is  added,  and  indifferent  substances  are 
then  added  for  the  purpose  of  diminishing  the  explosive 
force  of  the  powder  that  is  to  be  prepared,  and  if  the  greater 
part  of  the  acetone  is  then  removed  by  evaporation,  the 
substance  that  remains  can  be  made  into  long  threads  of  any 
9 


130  CHEMISTRY  IN   DAILY  LIFE 

desired  thickness  by  the  help  of  machines.  Cordite  is  pre- 
pared by  evaporating  the  rest  of  the  acetone  from  these 
threads;  this  smokeless  powder  (the  name  of  which  is  derived 
from  the  word  cord)  is  used  in  the  English  army.  The 
explosive  force  of  cordite  can  be  modified  by  adding  greater 
or  smaller  quantities  of  indifferent  substances  to  the  solution 
from  which  it  is  obtained. 

Many  attempts  have  naturally  been  made  to  prepare 
suitable  powders  or  explosives  by  methods  quite  different 
from  those  that  have  been  described.  If,  for  example,  the 
nitrogen  atom  in  saltpetre  is  replaced  by  an  atom  of  chlorine, 
the  new  compound  chlorate  of  potash  is  obtained.  Thus 

KN03  KC103 

Nitrate  of  potash.  Chlorate  of  potash. 

The  abbreviation  for  nitrogen  is  N,  the  first  letter  of  the  name  ;  the 
abbreviation  Cl  is  used  for  chlorine,  that  is  the  first  and  third  letters  of 
the  name.  The  formulae  which  are  written  with  the  help  of  these  con- 
tractions show  very  clearly  the  chemical  similarities  of  the  two  compounds 
we  are  speaking  of. 

Chlorate  of  potash  was  discovered  by  Berthollet  towards 
the  end  of  the  eighteenth  century.  He  proposed  that  it 
should  be  used  as  a  substitute  for  saltpetre.  The  French 
Government  attempted  to  make  gunpowder  containing  this 
compound.  The  manufacture  began  one  morning  ;  by  the 
afternoon  several  workmen,  and  a  lady  who  happened  to 
be  in  the  factory,  were  dead.  The  extraordinary  sensibility 
to  friction,  or  shock,  of  mixtures  containing  chlorate  of 
potash  made  it  impossible,  for  at  least  a  hundred  years, 
to  prepare  explosives  by  the  help  of  this  substance.  Never- 
theless, extremely  active  explosives  containing  chlorate  of 
potash  have  been  prepared  in  Germany  since  1908.  Oil  or 
wax  is  added  to  the  mixture ;  these  substances  diminish 
the  friction.  The  product  explodes  only  after  an  initial 


CELLULOID — ARTIFICIAL  SILK  131 

burning   has   been  started.      The   manufacture  can  be  con- 
ducted without  danger. 

Superficially  mixed  preparations  of  chlorate  of  potash  and 
similar  compounds  with  other  substances  are  employed  in 
making  fireworks  ;  these  mixtures  are  poured  into  covers, 
generally  of  a  cylindrical  shape,  in  which  they  are  gradually 
burned. 

We  must  not  omit  the  mention  of  some  of  the  applications 
of  nitrocellulose  to  peaceful  purposes.  The  manufacture  of 
artificial  silk  from  nitrocellulose  will  be  described  on  p.  134. 
In  1877  Hyatt  discovered  that  a  mixture  of  guncotton  and 
camphor  is  changed,  by  heat,  into  a  uniform,  horn-like 
substance,  which  can  be  shaped  into  any  desired  form,  and 
has  many  and  very  useful  properties.  This  substance,  under 
the  name  celluloid,  has  found  very  diverse  applications.  The 
great  drawback  to  the  use  of  celluloid  is  its  remarkable 
inflammability.  Nitrocellulose  is  made  by  treating  cotton- 
wool with  nitric  acid  ;  after  innumerable  experiments  it  was 
found,  in  1907,  that  by  using  acetic  acid  in  place  of  nitric 
acid  a  substance  is  obtained  which  so  far  resembles  nitro- 
cellulose that  it  may  be  used  to  prepare  a  sort  of  celluloid. 
This  substance  is  known  as  cellite ;  unlike  celluloid,  it  is 
difficult  to  set  fire  to. 

The  pieces  which  drop  off  in  making  celluloid  articles  are 
used  for  manufacturing  artificial  leather.  They  are  dissolved  in 
spirit,  oil  is  added,  and  cotton-cloth  is  steeped  in  the  liquid. 
When  the  spirit  is  evaporated  a  substance  is  obtained 
which  has  the  feel,  flexibility,  elasticity,  and  impermeability 
by  water,  of  leather.  By  passing  the  artificial  leather  through 
hot  rollers  the  grain  of  leather  is  so  well  imitated  that 
even  an  expert  cannot  distinguish  it  from  genuine  leather 
merely  by  looking  at  it.  The  discovery  of  this  method  of 
making  artificial  leather  was  made  by  Gevaert.  Because 


132  CHEMISTRY  IN   DAILY  LIFE 

of  the  constant  rise  in  the  price  of  leather  the  demand 
for  this  excellent  substitute  increases.  It  serves  well  for 
making  the  uppers  of  cheap  shoes. 

We  must  now  speak  of  the  substances  used  for  clothing. 
Substances  made  from  both  animal  and  vegetable  fibres  are 
used  for  this  purpose,  and  leather  is  also  employed. 

Fibres  of  animal  origin  are  very  different  chemically  from 
the  fibres  of  vegetable  substances,  inasmuch  as  the  former 
contain  nitrogen,  but  the  latter  do  not  contain  this  element. 
If  animal  fibres  catch  fire  they  produce  badly  smelling 
nitrogenous  substances — they  are  said  to  smell  like  burning 
horn ;  vegetable  fibres,  on  the  other  hand,  produce  a  smell 
like  that  of  burning  paper. 

We  have  naturally  but  little  to  say  here  about  the  fibres 
themselves.  The  most  important  things  made  from  animal 
fibres  are  wool  and  silk.  Wool  has  a  very  rough  surface  set 
with  many  little  projections.  Woollen  cloth  is  made  by 
stretching  woollen  threads  on  a  frame,  and  so  forming  the 
warp,  on  which  the  woof  is  spun  by  a  shuttle  which  flies 
to  and  fro  ;  the  cloth  made  in  this  way  is  very  similar  in 
appearance  to  stuff  made  of  strong  linen  fibres.  But  if  the 
material  is  now  wetted  and  worked  vigorously,  or  milled  as 
the  expression  is,  the  projections  of  the  single  threads  are 
kneaded  into  one  another — the  cloth  is  said  to  be  felted 
or  fulled — and  the  product  has  the  surface  we  are  accustomed 
to  perceive  on  woollen  goods.  The  processes  to  which  the 
cloth  is  then  subjected — shearing,  teaseling,  etc. — belong  to  the 
technical  details  of  the  manufacture,  and  do  not  interest  us 
here. 

The  properties  of  silk  do  not  allow  of  its  being  felted  ;  the 
single  threads  can  therefore  be  distinguished  in  finished 
silken  fabrics.  This  is  the  case  also  with  linen  and  cotton. 


SHODDY  133 

However  much  cotton  or  linen  goods  may  be  washed,  the 
single  threads  always  remain  side  by  side,  and  they  can  be 
separated  by  picking. 

But  artificial  wool,  mercerised  cotton-wool,  and  artificial 
silk  are  much  more  interesting  to  the  chemist  than  the 
materials  that  are  spun  from  the  natural  stuff. 

When  woollen  clothes  have  become  unfit  for  further  use 
because  of  constant  wear,  the  greater  part  of  the  wool 
that  was  used  in  making  them  still  remains  in  the  clothes  ; 
only  their  appearance  is  bad — they  have  gone  into  holes,  etc. 

It  is  easy  to  see  that  if  woven  goods,  such  as  hosiery,  are 
completely  picked  to  pieces — and  this  can  be  done  without 
trouble  by  a  machine — a  wool  will  be  obtained  which  may 
again  be  spun,  and  which,  although  not  equal  to  unused 
wool,  will  yet  be  of  some  service. 

Now  it  is  not  only  such  woollen  goods  that  are  picked  to 
pieces,  but  cast-off  wearing  apparel,  that  can  be  obtained  in 
much  greater  quantity,  is  also  treated  in  this  way.  All  the 
stitches  must  be  taken  out  of  the  clothes  before  they  are 
picked  to  pieces  by  the  machines.  This  preliminary  treat- 
ment is  done  by  workwomen.  The  odd  pieces  of  cloth  thus 
obtained  are  sorted,  and  then  pulled  to  pieces.  The  wool  is 
thus  got  out  of  the  cloth  ;  but  a  little  consideration  will  show 
that  the  threads  of  this  wool  will  be  much  shorter  than 
those  of  the  wool  from  which  the  cloth  was  originally  manu- 
factured. Nevertheless  this  wool  is  an  excellent  material  for 
weaving,  and  finds  a  very  suitable  use  in  making  up  those 
cheap  stuffs  which  are  purchased  by  people  that  are  not 
well-to-do. 

The  manufacture  of  such  stuffs  would  be  very  easy  were  it 
not  for  the  following  consideration.  Cotton  is  much  cheaper 
than  wool  ;  hence  some  cotton  is  generally  mixed  with  wool 
before  spinning,  in  order  to  reduce  the  price  of  the  articles 


134  CHEMISTRY  IN  DAILY  LIFE 

manufactured  therefrom.  But  as  wool  and  cotton  cannot  be 
dyed  equally  (the  reason  of  this  we  shall  learn  later)  it  is  not 
customary  to  mix  cotton  with  wool  in  a  casual  manner  ;  the 
practice  rather  is  to  make  the  warp  of  cotton  threads  and  the 
woof  of  wool.  When  the  cloth  is  milled  the  wool  is  mingled 
with  the  cotton  sufficiently  to  cover  and  so  to  hide  the  latter. 

It  is  only  at  those  parts  of  the  clothes  where  there  is  much 
wear — at  the  armholes,  for  instance — that  the  wool  soon 
gets  rubbed  off  and  the  tightly  twisted  separated  threads 
of  cotton  make  their  appearance.  If  such  clothes  are  again 
picked  to  pieces  to  make  artificial  wool — known  as  shoddy 
or  mungo — the  stuff  contains  cotton,  and  when  the  process 
has  been  repeated  several  times  the  material  becomes  quite 
useless. 

To  make  shoddy  that  contains  cotton  fit  for  use  the  cotton 
is  removed  by  a  process  known  as  " carbonising''  The  stuff 
is  placed  in  dilute  sulphuric  acid,  or  in  some  other  liquid 
/hich  acts  in  a  similar  way.  The  liquid  used  attacks  the 
cotton  in  the  material  in  such  a  way  that  after  drying  at  90° 
to  95°  C.  [194°  to  203°  F.]  the  cotton  is  disintegrated  to  a 
powder,  while  the  wool  is  practically  unaffected.  The  cotton 
can  then  be  completely  removed  by  working  up  the  material 
in  machines. 

Mercerised  cotton-wool  differs  from  the  ordinary  material 
in  its  silky  lustre.  The  preparation  of  it  is  fairly  simple. 
Tightly  stretched  cotton-wool  is  immersed  in  soda-lye  (about 
which  we  shall  learn  something  in  Lecture  VIII.),  and  is  then 
thoroughly  wasjied.  The  invention  depends  on  the  stretching 
of  the  cotton  ;  if  the  cotton  is  not  stretched  it  shrivels  up  and 
is  useless. 

The  preparation  of  artificial  silk,  a  name  applied  to  various 
lustrous  stuffs,  demands  much  more  skill  than  that  of 


ARTIFICIAL  SILK  135 

mercerised  cotton.  The  process  consists,  in  the  main,  in 
dissolving  cotton-wool,  or  nitrocellulose  made  from  cotton- 
wool, in  a  suitable  solvent,  and  causing  the  solution  to  flow 
from  a  very  fine  orifice  into  a  liquid  wherein  cotton-wool  and 
nitrocellulose  are  insoluble.  A  solution  of  a  compound  of 
copper,  to  which  much  ammonia  has  been  added,  dissolves 
cotton-wool ;  we  have  already  seen  that  there  are  many 
solvents  for  nitrocellulose  (p.  128).  The  threads  of  the 
material  thus  obtained  have  a  very  fine  lustre,  hence  the  name 
artificial  silk.  If  nitrocellulose  is  used,  the  product  is  a 
kind  of  smokeless  powder  (p.  126);  it  must  be  treated  with 
chemical  substances  which  remove  the  nitrogroups,  a  process 
of  no  especial  difficulty.  Because  of  its  exceedingly  fine  lustre, 
large  quantities  of  artificial  silk  have  been  used  for  decorative 
purposes. 

It  is  interesting  to  know  that,  by  forming  coarser  threads,  a 
very  good  imitation  of  human  hair  is  produced,  instead  of 
artificial  silk.  Excellent  artificial  horsehair  has  also  been 
made.  In  the  beginning  of  1908  twenty-two  factories  of 
artificial  silk  had  been  established. 

Most  of  the  fibres  that  are  spun  into  materials  are  colour- 
less as  they  occur  naturally.  But  as  it  would  not  always 
be  convenient  to  wear  white  garments  the  practice  of  dyeing 
materials  has  prevailed  since  early  times. 


LECTURE   VII 

Tanning — Leather — Removing  hair  from  hides  and  softening  them — 
Tanning  materials — Barks — Quebracho  bark — Sumac — Tanning 
extracts — Sole  leather — Alum  tanning — Glove  leather — Furriery — 
Iron  and  chrome  leather — Chamois  leather — Wash  leather — 
Parchment — Bleaching  on  meadows — Blueing  washed  linen — 
Bleaching  by  chlorine — Bleaching  powder — Antichlors — Rau  de 
Javelle — Sulphurous  acid — Persil — Dyeing  —  Mordants — Lakes — 
Substantive  colours — Coal  tar  colours  — Indigo — Alizarin— Colour- 
ing pastes — Colouring  extracts  from  woods — Log-wood — Calico 
printing. 

BEFORE  dealing  with  the  subject  of  dyeing  it  is  advisable  to 
say  something  about  the  preparation  of  leather,  which,  being 
the  substance  that  serves  as  a  covering  for  our  feet,  naturally 
finds  a  place  after  those  materials  that  are  woven  from 
threads  and  made  into  clothing.  For  many  other  purposes 
of  ordinary  life  also  nothing  can  be  substituted  for  leather. 

Leather  is  the  skin  of  animals  which  is  so  changed,  by  the 
process  of  tanning,  that  it  neither  putrifies  nor  becomes  hard 
when  it  is  dried. 

Fresh  skins  of  animals  are  extremely  liable  to  undergo 
putrefaction.  They  lose  this  tendency  when  they  are  dried  ; 
but  the  dry  skins  are  hard  and  brittle  because  their  fibres  are 
glued  together.  In  the  process  of  tanning  the  tanning 
material  is  brought  between  the  fibres,  and  so  prevents  the 
adherence  of  those  fibres  to  one  another ;  leather  is  thus  pro- 
duced the  pliability  of  which  is  more  or  less  like  that  of  the 
skins  of  living  animals. 

136 


TANNING  137 

The  first  thing  to  be  done  with  skins  that  are  to  be 
used  for  making  leather  is  to  remove  the  hair  from  them. 
The  oldest  method  for  doing  this  is  known  as  "  sweating" ; 
this  method  is  still  used  to  some  extent  in  an  improved  form 
to-day.  The  process  consists  in  leaving  the  moistened  skins 
or  hides  for  some  time  by  themselves ;  a  slight  putrefaction 
occurs  which  so  softens  the  hair  that  it  can  be  scraped 
off  without  much  trouble.  The  sweating  is  stopped  as  soon 
as  the  hair  is  softened  sufficiently.  The  process  of  loosening 
the  hair  can  also  be  easily  accomplished  by  the  aid  of 
chemicals  ;  and  burnt  lime  has  long  been  used  for  this 
purpose.  The  lime  is  slaked  with  a  large  quantity  of  water 
(we  shall  have  to  deal  with  the  slaking  of  lime  when  we 
come  to  speak  of  mortar),  and  the  hides  are  steeped  in 
the  milk  of  lime  thus  obtained.  A  compound  of  sulphur  and 
lime,  or  the  chemically  similar  compound  sulphide  of  soda, 
is  a  more  effective  depilatory  than  lime.  These  substances 
are  now  manufactured  especially  for  the  purpose  of  removing 
the  hair  from  hides  that  are  to  be  made  into  leather. 

After  the  hair  has  been  removed  the  hides  are  soaked 
in  some  liquid  which  takes  away  any  lime  that  still  adheres 
to  them,  because  if  this  lime  were  allowed  to  remain  in  the 
hides  it  would  interfere  with  the  tanning  processes.  Very 
dilute  acid — sulphuric  acid,  for  instance — may  be  used  for 
this  purpose ;  when  soaked  in  such  a  bath  the  hides  swell 
up  to  twice  their  original  thickness,  and  so  become  more 
easily  permeated  by  the  tanning  materials. 

It  is,  however,  customary  to  employ  a  method  that  has 
been  handed  down  from  ancient  times,  and  which  is  purely 
empirical.  The  acid  bath  is  prepared  by  the  process  of 
lactic  fermentation,  with  which  we  are  already  familiar ;  the 
result  is  found  to  be  more  satisfactory  than  when  the  bath  is 
made  of  any  one  of  the  dilute  acids  that  have  been  tried 


138  CHEMISTRY  IN   DAILY  LIFE 

for  this  purpose.  The  bath  is  prepared  by  steeping  wheat 
bran  in  water,  adding  sour  dough,  and  allowing  the  lactic 
fermentation  to  complete  itself  at  about  50°  C.  [120°  F.].  As 
we  already  know,  small  quantities  of  other  acids  besides 
lactic  acid — butyric  acid,  for  instance — are  produced  by  this 
process  (see  p.  85). 

When  the  hides  are  steeped  in  this  bath,  after  the  liquor 
has  become  cold,  they  swell  up  and  become  ready  to  absorb 
the  tanning  substances  from  the  materials  used  in  the  next 
stage  of  the  process. 

Tanning  substances — that  is  to  say,  substances  which 
convert  the  skins  of  animals  into  leather — are  found  in 
very  many  plants.  One  speaks,  for  example,  of  the  tannin 
of  tea  and  coffee.  The  high  price  of  such  plants  as  those  that 
produce  tea  or  coffee  of  course  negatives  the  employment 
of  these  materials  in  leather  making.  Barks  are  the  most 
commonly  used  materials,  and  especially  the  bark  of  the  oak, 
which,  when  cut  into  small  pieces,  is  known  as  oak  tan, 
or  simply  tan.  The  trees  are  barked  when  they  are  from 
fifteen  to  twenty  years  old,  as  the  proportion  of  bark  to  wood 
is  greatest  at  that  period  of  their  growth. 

To  prevent  the  unnecessary  withdrawal  of  energy  from  the 
soil — which  means,  as  we  now  know,  the  uncalled-for  removal 
of  inorganic  salts — the  wood  of  the  trees  is  burnt  on  the  spot, 
and  the  ashes  go  to  enrich  the  soil.  Of  course  the  soil  may 
also  be  enriched  by  the  use  of  artificial  manures. 

The  barks  of  firs,  pines,  and  in  many  places  also  the  bark 
of  the  walnut  tree  are  employed  for  tanning,  besides  oak 
bark  ;  but  these  are  generally  mixed  with  oak  bark  before 
use.  In  consequence  of  the  large  quantities  of  leather  that 
are  used  nowadays  substitutes  for  bark  are  derived  from 
other  sources,  especially  from  certain  foreign  trees  and  shrubs, 
for  the  tanning  substances  are  found  in  other  parts  of  plants 


TANNING  139 

besides  the  bark.  The  only  one  of  these  woods  we  shall 
mention  is  quebracho  wood.  This  is  a  very  hard,  dark  red 
wood,  which  is  exported  in  large  quantities  from  Argentina  ; 
after  it  has  been  rasped  to  pieces  by  a  machine  it  is  used 
in  the  same  way  as  oak  bark. 

Sumac  is  also  much  used.  It  is  a  powder  made  by  rubbing 
the  young  dried  shoots  of  plants  of  the  Rhus  order  which 
grow  in  the  southern  parts  of  Europe.  But  we  need  not 
make  any  further  enumeration  of  the  materials  used  in 
tanning. 

Tanning  with  oak  bark,  or  a  substitute  for  bark,  is  con- 
ducted by  placing  the  swollen  hides  and  the  tanning  material 
in  alternate  layers  in  a  pit  until  the  pit  is  full,  and  then 
running  in  water  sufficient  to  cover  the  whole  of  the  contents. 
The  tanning  substances  gradually  pass  into  solution,  and 
they  are  slowly  absorbed  by  the  hides.  As  thick  hides 
require  very  large  quantities  of  tanning  material,  they  must 
be  mixed  repeatedly  with  fresh  layers  of  tan ;  the  process 
therefore  occupies  a  long  time,  even  as  much  as  two  years  or 
more ;  but  for  that  reason  the  product  is  excellent. 

Naturally  attempts  have  been  made  to  shorten  the  process  ; 
and  it  has  been  found  possible  to  complete  the  making 
of  leather  in  about  three  months  by  extracting  the  tanning 
material  with  water  and  then  steeping  the  hides  in  the  liquor 
thus  obtained. 

This  brings  us  to  the  consideration  of  extracts  used  in 
tanning.  Such  extracts  have  been  sent  on  to  the  market  for 
many  years  from  the  East  Indies,  where  they  are  prepared  by 
extracting  suitable  woods  or  leaves  with  water,  and  then 
evaporating  as  far  as  possible  so  as  to  decrease  the  cost 
of  transport ;  the  most  important  of  these  extracts  are  known 
as  gambier  and  catechu.  Similar  extracts  have  been  prepared 


I4O  CHEMISTRY  IN   DAILY  LIFE 

in  Europe  since  the  year  1882,  and  the  cost  of  carriage  of 
tanning  materials  has  thereby  been  much  diminished  ;  extract 
of  oak  bark,  for  instance,  comes  from  Hungary  and  Croatia, 
extract  of  chestnut  bark  from  Corsica,  and  extract  of  que- 
bracho wood  from  Argentina  and  the  European  seaport  towns 
to  which  the  wood  is  brought.  The  manufacture  is  carried  on 
by  rasping  or  grinding  the  material,  exhausting  with  water, 
and  evaporating  the  aqueous  solution  thus  obtained.  The 
evaporation  is  not  effected  in  open  vessels,  but  under  greatly 
reduced  pressure  in  a  way  like  that  followed  in  making  sugar, 
about  which  we  have  already  learnt  something  (see  p.  75). 
This  method  preserves  all  the  desirable  properties  of  the 
extracts,  which  could  not  be  done  were  the  evaporation 
conducted  in  the  ordinary  manner. 

The  preparation  of  leather  by  the  use  of  such  extracts  is  a 
much  less  troublesome  process  than  the  manufacture  by  the 
older  methods ;  and  the  process  is  also  quickened  to  an 
extent  that  is  quite  astonishing. 

A  German  patent  of  1892  asserts  that  the  thickest  sole 
leather  can  be  made  in  thirty-six  hours,  by  treating  soaked 
hides  with  an  extract  liquor  eight  times  more  concentrated 
than  that  generally  employed,  in  a  machine  which  revolves 
about  ten  times  per  minute.  Instead  of  requiring  a  couple 
of  years,  as  was  formerly  the  case,  prepared  hides  can  now 
be  made  into  leather  in  less  than  two  days ;  and  this  patent 
is  not  impracticable,  as  many  patents  are,  for  sole  leather 
made  by  this  method — and  it  is  only  for  sole  leather  that 
the  process  seems  to  be  suitable — has  taken  a  firm  place 
on  the  market. 

Besides  the  methods  of  tanning  that  we  have  been  speaking 
of  there  are  two  other  processes  that  are  much  used  ;  these 
are  alum  tanning  and  chamois  leather  tanning. 

Chemically   considered,   alum   is   a   double   compound   of 


TANNING  141 

sulphate  of  potash  and  sulphate  of  alumina.  When  soaked 
and  cleaned  hides  are  brought  into  a  solution  of  alum  to 
which  common  salt  has  been  added,  the  alumina  acts  in  the 
same  way  as  the  tanning  substances  do  which  we  have 
already  considered  ;  the  alumina  penetrates  the  hides  and  by 
its  deposition  between  the  fibres  prevents  the  hardening 
of  the  material  which  is  subjected  to  this  tanning  operation. 
When  this  product  is  thoroughly  rubbed  and  worked  with 
fat,  the  fat  is  taken  into  the  substance,  and  the  material 
thus  obtained  is  the  most  tenacious  kind  of  leather  that  is 
known. 

The  leather  for  kid  gloves  is  made  in  this  way,  working 
with  very  great  care  to  prevent  the  formation  of  spots,  etc., 
and  using  the  skins  of  young  animals,  especially  those  of  kids 
and  lambs.  The  tanning  liquor  used  for  this  purpose  consists 
of  a  solution  of  alum  to  which  egg  yolks  and  meal  have  been 
added.  Egg  yolk  consists  chiefly  of  albumen  and  fat,  the 
latter  being  present  in  an  extremely  finely  divided  state  ;  and 
it  is  to  the  thorough  permeation  of  the  skins  by  this  finely 
divided  fat,  along  with  the  tanning  material,  that  the 
remarkable  pliability  of  kid  glove  leather  is  due. 

Although  alum  or  white  tanning  is  not  nearly  so  effectual 
as  tanning  by  oak  bark,  nevertheless  there  are  many  purposes 
for  which  the  latter  cannot  be  used.  The  leathers  made  by 
these  two  methods  show  great  differences  in  their  behaviour 
towards  water.  Experience  in  the  wearing  of  boots  shows 
us  that  good  sole  leather  is  impervious  to  water ;  but  the 
tanning  matter  is  nearly  all  withdrawn  from  white  tanned 
leather  by  the  action  of  a  large  quantity  of  water.  We  know, 
for  instance,  that  when  gloves  get  very  wet  they  shrivel,  and 
behave  like  untanned  skins. 

Alum  is  also  employed  in  the  tanning  of  skins  to  be  used 
as  furs.  The  details  of  the  various  processes  differ  much 


142  CHEMISTRY  IN   DAILY  LIFE 

but  the  method  is  essentially  a  tannage  by  fat  and  alum. 
Speaking  generally,  the  skins  are  thoroughly  cleaned  with 
soap,  then  dried,  and  then  fat  is  rubbed  on  to  their  inner 
sides  and  worked  in  as  thoroughly  as  possibly  and  as  long  as 
any  of  it  is  absorbed  ;  the  skins  are  then  placed  in  a  sour 
bran-drench,  which  causes  a  slight  swelling  after  about  twenty- 
four  hours ;  the  bran  is  then  removed,  and  the  tanning  is 
effected  by  a  solution  of  alum  and  common  salt 

Alumina  is  a  base  (see  p.  49) ;  hence  it  does  not  seem 
absurd  to  suppose  that  other  bases  might  be  substituted  for 
alumina  in  tanning,  and  that  new  kinds  of  leather  might 
thus  be  produced.  A  consideration  of  the  properties  of 
various  bases  by  experts  led  to  the  conclusion  that  there  are 
only  two  which  would  be  worth  trying,  and  these  are  oxide 
of  iron  and  oxide  of  chromium.  As  a  fact  leather  has  been 
prepared  by  using  these  bases  ;  but  only  the  second  has 
continued  to  be  used.  Chrome  leather  is  soft  and  supple  ; 
and  as  it  is  more  impervious  to  moisture  and  resists  high 
temperatures  better  than  other  sorts  of  leather,  it  has  come 
into  lasting  use.  Indeed,  in  1908  the  three  largest  German 
makers  of  upper  leathers  announced  that  they  would  not 
require  any  more  oak-bark. 

We  have  still  to  speak  of  cJiamois  or  oil  tanning.  Here 
also  the  skins  are  freed  from  hair,  and  are  swollen  ;  they  are 
then  rubbed  with  fat,  fish  oil  or  whale  oil  being  the  form  of 
fat  that  is  used,  and  afterwards  they  are  thoroughly  fulled, 
and  are  again  rubbed  with  oil  as  long  as  any  is  absorbed. 
The  absorption  of  the  oil  is  not  altogether  a  mechanical 
process ;  a  chemical  change  also  occurs,  and  this  is  accom- 
panied by  the  production  of  a  definite  smell  which  indicates 
that  the  operation  is  completed.  The  skins  are  then  allowed 


WASH  LEATHER — PARCHMENT  143 

to  remain  for  some  time  in  heaps,  where  they  become  warm 
owing  to  the  heat  produced  by  the  chemical  changes  that 
continue  to  occur ;  the  rise  of  temperature  favours  the 
chemical  reactions,  which  proceed  more  rapidly  until  at  last 
the  skins  acquire  a  yellow  colour.  The  result  of  this 
treatment  is  that  the  fibres  become  so  enveloped  in  fatty 
matter  that  they  no  longer  adhere  together — a  true  leather  is 
produced — and  the  combination  of  the  fibres  with  the  fat  is 
so  intimate  that  even  hot  water  is  not  able  to  dissolve  it ; 
for  this  reason  the  leather  is  called  wash  leather.  The  leather 
is  then  washed  with  potash  solution  to  remove  the  surplus 
fat  that  remained  chemically  uncombined  when  the  yellowing 
of  the  skins  began.  This  fat  forms  an  emulsion  with  the 
potash,  and  is  removed  by  washing  with  water.  If  the  potash 
in  the  emulsified  liquor  is  neutralised  with  acid  the  fat  rises 
to  the  top  of  the  liquor.  This  fat  is  found,  by  experience, 
to  be  very  suitable  for  rubbing  into  leather  prepared  by  the 
methods  of  tanning  described  in  the  earlier  part  of  this 
lecture  ;  it  comes  into  commerce  under  the  name  of  degras. 

Furs  are  also  sometimes  prepared  by  the  methods  used  in 
making  chamois  leather. 

Parchment  should  be  mentioned  here.  Although  parchment 
is  often  supposed  to  be  a  leather,  yet  it  is  not ;  it  is  prepared 
by  removing  the  hair  from  the  skins  of  very  young  animals 
by  means  of  lime,  then  cleaning  the  skins  thoroughly  and 
drying  them  while  they  are  stretched  tightly.  To  give  the 
dried  skins  a  smooth  surface  they  are  sprinkled  with  chalk 
and  rubbed  with  pumice  stone.  The  product  is  too  smooth 
for  writing  on,  and  therefore,  if  it  is  not  to  be  used  for 
binding  books,  making  drums,  or  some  such  purpose,  it  is 
brushed  over  with  thin  white  oil  paint  so  as  to  produce 
a  surface  that  can  be  written  upon. 


144  CHEMISTRY  IN  DAILY  LIFE 

We  must  now  return  to  textile  fabrics  that  we  may  consider 
the  bleaching  and  dyeing  of  these  materials.  In  connection 
with  dyeing  we  shall  have  something  to  say  about  painting. 
White,  or  nearly  white,  is  the  natural  colour  of  the  materials 
that  are  woven  in  linen,  cotton,  and  woollen  goods,  and 
the  like. 

It  would  not  be  altogether  pleasant  to  wear  white  clothes, 
because  their  appearance  soon  becomes  disagreeable  ;  besides 
this,  coloured  stuffs  confer  a  more  beautiful  and  more 
distinguished  appearance,  as  was  recognised  in  the  olden 
days  when  a  red-purple  mantle  was  worn  only  by  the  chief 
men.  Careful  investigations,  made  since  1908,  of  the  shellfish 
from  which  purple  dye  was  obtained  by  the  ancients  have 
shown  that  the  purple  then  used  must  have  had  a  rather  dis- 
agreeable blue-black  tinge. 

Most  of  the  natural  materials  that  are  woven  have  a  shade 
of  yellow  in  them,  and  the  object  of  bleaching  these  materials 
in  the  sunshine  is  to  remove  this  colour.  This  yellowish 
coloration  is  removed,  as  most  colours  are,  by  exposure  to 
sunshine ;  the  process  whereby  the  yellow  is  changed  into 
pure  white  is  hastened  by  blueing  the  goods — this  is  practised 
with  the  household  washed  linen,  for  instance.  Yellow  and 
blue  are  complementary  colours,  and  they  neutralise  one 
another. 

When,  in  course  of  time,  the  making  of  linen  and  cotton 
fabrics  passed  from  the  hands  of  individual  home-workers, 
and  the  manufactures  became  concentrated  in  factories,  it 
was  necessary  to  provide  very  large  bleaching  grounds  for 
the  goods,  and  this  involved  much  trouble  and  expense, 
some  districts,  indeed,  where  the  manufacture  of  these  goods 
has  advanced  very  much,  it  would  be  quite  impossible  to 
provide  sufficiently  large  bleaching  grounds.  Nowadays,  and 
indeed  since  the  discovery  of  artificial  bleaching  stuffs,  all 


In 
>ds'-<, 


BLEACHING  145 

linen  and  cotton  fabrics  are  bleached  in  the  factories,  by  the 
use  of  chloride  of  lime. 

Chlorine  is  a  gas  which  shows  a  very  marked  readiness  to 
combine  with  other  bodies.  It  was  not  until  some  time  after 
its  discovery,  in  the  last  quarter  of  the  eighteenth  century, 
that  this  substance  was  recognised  to  be  a  distinct  elementary 
body.  Because  of  its  great  activity — an  activity  greater  even 
than  that  of  oxygen,  which  was  the  most  active  substance 
known  at  the  time  of  the  discovery  of  chlorine— the  gas  was 
supposed  to  be  a  new  kind  of  oxygen,  and  the  French 
chemists  of  that  period  often  spoke  of  nouvel  oxygene.  In 
consequence  of  its  energetic  action  on  the  most  different  kinds 
of  substances,  chlorine  destroys  the  greater  number  of 
colouring  substances. 

The  employment  of  gaseous  substances  in  factory  industries 
is  very  inconvenient ;  for  this  reason  chlorine  is  not  itself 
used  as  a  bleacher,  but  the  compound  is  employed  which 
chlorine  forms  with  lime  when  it  is  passed  over  that  substance. 
This  compound,  which  was  first  prepared  in  1799  by  Tennant 
in  Glasgow,  is  known  as  chloride  of  lime  [or  as  bleaching 
powder}.  At  first,  1000  kilograms  of  bleaching  powder  cost 
2800  marks;  in  1820,  only  540  marks;  and  at  present, 
about  no  marks.  [About  .£140,  £27,  and  £5  icxr.  per  ton."] 
When  bleaching  powder  is  shaken  with  water,  the  insoluble 
parts  of  the  powder  sink  on  standing,  and  a  clear  solution  of 
the  bleaching  substance  is  obtained.  If  lime  is  added  to  this 
liquid,  and  chlorine  is  passed  into  it,  crystallised  chloride  of 
lime  separates.  This  substance  has  become  a  commercial 
product  since  1907 ;  it  is  much  more  effective  than  ordinary 
bleaching  powder. 

The  bleaching  action,  or,  to  use  a  more  accurate  expression, 
the  chemical  energy,  of  this  substance  destroys  the  yellowish 
tint  of  white  linen  or  cotton  goods  in  a  very  short  time,  and 
10 


146  CHEMISTRY  IN    DAILY  LIFE 

as  effectually  as  the  process  of  bleaching  on  meadows.  But 
the  energy  of  the  bleaching  powder  is  not  exhausted  by  this 
process ;  having  destroyed  the  colour,  the  bleaching  powder 
attacks  the  fibres  of  the  goods — and  it  is  for  this  reason  that 
the  use  of  bleaching  powder  has  never  found  favour  with 
housewives.  In  factories,  however,  matters  are  managed 
differently  ;  as  soon  as  the  goods  are  bleached  the  excess  of 
chlorine  is  rendered  inactive  by  addition  of  an  antichlor,  and 
the  fibres  of  the  goods  are  not  injured  in  the  slightest. 
Many  and  very  different  chemical  substances  may  be 
employed  as  antichlors ;  the  most  commonly  used  is 
hyposulphite  of  soda.  This  salt  has  no  action  on  washed 
linen,  and  as  soon  as  it  comes  into  contact  with  chloride 
of  lime  it  forms  new  compounds  which  are  also  without 
action  on  the  linen,  and  at  the  same  time  the  chloride  of 
lime  is  converted  into  the  perfectly  harmless  chloride  of 
calcium. 

In  addition  to  chloride  of  lime,  the  substance  known  as 
eau  de  Javelle  is  used  commercially  as  a  bleaching  agent. 
The  difference  between  these  two  substances  is  that  the 
eau  de  Javelle  contains  soda  in  place  of  lime ;  the  chemical 
action  of  the  one  is  practically  the  same  as  that  of  the  other. 
If  eau  de  Javelle  is  used — and  it  is  in  favour  for  removing 
stains,  which  it  gradually  destroys — a  small  quantity  of 
an  antichlor — a  little  hyposulphite  of  soda  dissolved  in  water, 
for  instance — should  be  put  on  the  cloth  after  the  cleaning 
has  been  effected,  as  if  this  is  not  done  the  fibres  will  be 
rotted. 

Chloride  of  lime  cannot  be  employed  for  bleaching  fabrics 
woven  from  animal  fibres,  because  it  does  not  thoroughly 
bleach  such  fabrics,  but  only  turns  them  yellow.  Sulphurous 


BLEACHING  147 

acid,  which  is  a  less  energetic  bleaching  agent  than  chloride 
of  lime,  is  employed  for  taking  away  the  colour  from  animal 
fabrics. 

Sulphurous  acid  is  the  sharply  smelling  gas  that  is  formed 
when  sulphur  is  burnt.  As  the  gas  is  very  soluble  in  water, 
the  usual  method  of  working  is  to  hang  the  goods,  after 
wetting  them,  in  a  chamber  wherein  sulphur  is  burnt.  No 
special  means  of  destroying  the  excess  of  sulphurous  acid 
is  required,  because,  when  this  method  is  adopted,  only  a 
very  little  sulphurous  acid  ever  gets  into  each  piece  of  goods. 

We  have  still  to  mention  hydrogen  peroxide.  The  word 
peroxide  tells  that  the  compound  contains  much  oxygen.  It 
is  to  the  excess  of  oxygen  that  the  bleaching  power  of  the 
substance  is  due. 

This  substance  can  be  used  as  a  bleaching  agent  in  many 
cases  where  chloride  of  lime  and  sulphurous  acid  are  in- 
effectual :  it  is  employed  especially  for  bleaching  hair,  feathers, 
and  ivory.  Of  late  years  peroxides  have  been  more  widely 
used  for  bleaching.  For  a  time,  a  mixture  of  sodium  peroxide, 
soap,  and  soda  was  employed  ;  but  this  has  been  superseded 
by  Persil,  which  contains  10  per  cent,  of  boron  peroxide.  By 
mixing  persil  with  the  liquor  in  which  white  goods  are  washed, 
the  goods  are  at  once  washed  and  bleached.  Persil,  however, 
quickly  destroys  some  of  the  colours  of  dyed  cotton  and 
woollen  goods.  It  is  only  since  the  introduction  of  the  electric 
current  into  manufacturing  chemistry  that  it  has  become 
possible  to  prepare  peroxides  cheaply. 

We  have  now  to  consider  the  dyeing  of  textile  fabrics. 
This  part  of  the  subject  falls  into  two  main  divisions  :  the 
uniform  dyeing  of  the  whole  of  a  piece  of  goods,  and  calico 
printing. 


CHEMISTRY  IN   DAILY  LIFE 

The  simplest  way  of  dyeing  uniformly  a  piece  of  cloth 
would  be  to  mix  the  colour  with  glue  in  water  and  to  smear 
this  over  the  goods ;  but  the  colour  would  be  very  loosely 
retained,  and  the  cloth  would  have  to  be  protected  from  wet. 
Cloth  treated  in  this  way  would  rather  be  described  as 
coloured  than  as  dyed  :  the  colour  is  retained  better  if  it  is 
mixed  with  albumen  and  spread  over  the  cloth,  and  the  cloth 
is  then  heated  ;  the  albumen  is  coagulated,  and  is  thus 
rendered  insoluble  in  water.  Although  the  colour  is  fairly 
well  held  by  the  cloth,  still  much  of  it  is  removed  when  the 
cloth  is  rubbed  vigorously. 

This  process,  which  is  not  a  dyeing  process  in  the  proper 
meaning  of  the  term,  plays  a  certain  part  in  calico  printing. 
It  is  applicable  only  when  a  solution  of  the  colouring  matter 
acts  upon  the  fibres  of  the  material.  There  are  great  differ- 
ences in  this  respect ;  animal  fibres,  such  as  wool  and  silk, 
behave  towards  dye-stuffs  very  differently  from  vegetable 
fibres,  of  which  cotton  is  the  most  important. 

If  a  dye-stuff,  say  fuchsin,  is  dissolved  in  water,  and  a 
piece  of  wool  or  a  piece  of  silk  is  drawn  through  this  solution, 
the  colouring  matter  slowly  passes  from  the  solution  into  the 
fibres,  which  it  colours  red.*  But  if  we  place  cotton  in 
the  same  solution  we  find  that  the  vegetable  fibres  have  not 
the  property  of  retaining  the  colouring  substance.  For  if  we 
now  wash  the  red  coloured  wool  or  silk  with  much  water  the 
colour  is  still  retained  by  the  material  ;  but  when  the  cotton 
is  treated  in  the  same  way  it  returns  to  its  original  whiteness. 
All  dye-stuffs  cannot,  however,  be  applied  to  wool  and  silk 
so  easily  as  this.  In  wool  and  silk  dveirrg  it  is  generally 

*  The  fibres  play  here  somewhat  the  same  jiart  as  we  found  was  taken 
by  animal  charcoal  (see  p.  42).  In  the  same  way  as  animal  charcoal 
withdraws  the  colouring  substances  from  liquids — from  red  wine,  for 
instance — animal  fibres  are  able  to  combine  with  colouring  matters  and  to 
retain  these  firmly. 


DYEING  WITH  MORDANTS  149 

necessary  to  make  use  of  the  method  which  was  the  only 
practicable  method  for  dyeing  cottons  till  the  year  1884  ;  it  is 
necessary  to  use  mordants.  What  mordants  are  will  be  best 
understood  by  the  following  considerations. 

If  a  solution  containing  iron  is  added  to  a  solution  of 
yellow  prussiate  of  potash  the  beautiful  blue  substance  known 
as  Prussian  blue  is  precipitated.  Now  the  best  way  of  dyeing 
a  cloth  with  Prussian  blue  is  to  dip  the  cloth  first  into 
one  of  the  two  solutions  and  then  into  the  other.  If  the 
cloth  has  been  soaked  in  the  iron  solution  before  it  is 
immersed  in  the  solution  of  yellow  prussiate,  then  the  blue 
precipitate  is  formed  in  the  fibres  of  the  cloth,  that  is  to 
say,  the  colouring  matter  is  deposited  in  the  interior  of 
the  cloth,  and  as  the  precipitate  is  quite  insoluble  in  water 
it  is  not  removed  by  washing  even  with  much  water,  and 
hence  the  cloth  is  not  decolourised.  The  fabric  is  really 
dyed  by  this  process. 

The  use  of  mordants  is  based  on  such  a  process  as  that 
which  has  just  been  described.  The  stuff  to  be  dyed  is  first 
dipped  into  a  liquid  called  the  mordant,  which  introduces 
into  the  fibres  of  the  cloth  a  substance  that  reacts  with  the 
special  dye-stuff  to  be  used  and  produces  a  compound  which 
is  insoluble  in  the  mordant. 

Alumina  is  very  much  used  as  a  mordant.  In  dealing 
with  tanning  (see  p.  141)  we  found  that  alumina  is  able 
to  enter  into  combination  with  animal  fibres  ;  in  a  similar 
way  this  substance  shows  a  tendency  to  combine  with  both 
animal  and  vegetable  textile  fabrics  when  these  are  passed 
through  a  properly  prepared  solution  of  it. 

Alum,  which  is  a  double  compound  of  sulphate  of  alumina 
and  sulphate  of  potash  (see  p.  141),  was  formerly  a  very 
important  substance  in  dyeing,  inasmuch  as  it  was  the 


150  CHEMISTRY  IN   DAILY  LIFE 

only  soluble  salt  of  alumina  that  was  also  easily  procurable. 
This  compound  has  been  prepared  since  ancient  times  by 
an  easy  process  from  a  kind  of  earth  which  is  found  in 
certain  parts  of  Europe.  As  the  sulphate  of  potash  in  alum 
is  useless  for  the  purposes  for  which  the  alum  is  to  be 
employed  in  dyeing,  chemistry  has  long  ago  replaced  this 
double  salt  by  various  other  soluble  compounds  of  alumina. 

Now  if  cotton,  for  instance,  is  mordanted  by  being  dipped 
into  an  alumina  solution,  and  if  it  is  then  passed  through  a 
solution  of  fuchsin,  the  fabric  is  dyed  a  fast  red  ;  for  the  fuchsin 
is  deposited  in  the  fibres  of  the  fabric  in  the  form  of  an 
insoluble  compound  with  the  alumina,  and  the  process  is  quite 
similar  to  what  occurred  when  we  dyed  with  Prussian  blue. 

The  name  lakes  is  given  to  the  compounds  that  mordants 
form  with  dyes.  Of  course  we  can  produce  a  lake  without 
using  fibres  :  for  instance,  if  we  pour  a  solution  of  fuchsin 
into  a  solution  of  alumina  a  red  precipitate  is  obtained  ; 
and  if  we  dry  this  lake  and  then  rub  it  up  with  varnish 
(see  forward,  p.  161)  we  have  a  colour  ready  for  painting 
wherewith  we  can  cover  surfaces  in  any  way  we  desire. 

Alumina  is  a  base,  and  there  are  many  other  bases 
that  may  be  used  in  dyeing  in  the  same  way  as  alumina 
is  used.  Matters  are  different  here  from  what  we  found 
them  to  be  in  leather  making,  where  alumina  was  almost 
the  only  practically  useful  base  (see  p.  141).  It  is  not 
only  the  bases  that  we  are  all  familiar  with,  oxide  of  iron 
and  oxide  of  chromium,  that  play  important  parts  as 
mordants,  but  there  also  are  a  great  number  of  other  oxides 
suitable  for  holding  fast  the  dyes  in  the  fibres  of  fabrics. 
There  is,  for  instance,  oxide  of  tin,  which  is  used  in  the 
form  of  a  solution  of  chloride  of  tin,  or  as  it  is  commonly 
called  tin  composition. 


DYEING   WITH   MORDANTS  15! 

Tin  is  not  a  very  cheap  metal  to-day,  and  in  former  times 
it  was  extremely  costly.  Nevertheless  this  metal  began 
to  play  a  great  part  in  dyeing  after  the  discovery,  made 
accidentally  in  1640,  in  Holland,  that  the  most  beautiful  scarlet 
the  world  had  seen  was  produced  by  dyeing  with  cochineal 
after  mordanting  with  a  solution  of  tin  ;  and  the  importance 
of  tin  increased  when  it  was  found  at  a  later  time  that  it  had 
the  property  of  increasing  the  brilliancy  of  many  other  dyes. 
Although  more  beautiful  scarlets  have  been  dyed  in  the  last 
thirty  years  or  so  by  the  use  of  aniline  colours  than  could  be 
obtained  from  cochineal,  nevertheless  tin  has  retained  its  im- 
portance in  the  dyeing  industries  because  it  is  an  extremely 
suitable  reagent  for  fixing  the  most  different  kinds  of 
dyes. 

Besides  the  metallic  oxides  which  are  precipitated  in  the 
fibres  of  goods,  and  concerning  the  chief  of  which  we  have 
now  learnt  something,  there  is  another  important  mordanting 
material  known  as  tannin. 

Tannin  forms  lakes  directly  with  solutions  of  various  dye- 
stuffs,  so  that  goods  can  be  dyed  with  the  help  of  tannin.  In 
addition  to  this,  goods  that  have  been  treated  with  tannin  are 
sometimes  passed  through  solutions  of  alumina  or  other 
similar  oxides ;  compounds  of  tannic  acid  with  alumina  (or 
the  other  oxide)  are  thus  formed  in  the  fibres,  and  if  after  this 
double  mordanting  the  goods  are  dipped  into  various  dyeing 
solutions,  lakes  are  formed  that  are  composed  of  tannin, 
metallic  oxide,  and  the  dye.  With  the  help  of  tannin  most 
remarkable  results  can  now  be  obtained. 

We  said  above  that  no  practical  method  for  dyeing  cotton 
goods  without  using  mordants  existed  before  the  year  1884, 
and  that  however  simple  may  be  the  theory  of  mordants  the 
process  of  dyeing  by  their  use  requires  much  practice.  For 


152  CHEMISTRY   IN   DAILY  LIFE 

instance,  it  is  a  very  difficult  matter  to  fix  the  celebrated  red 
dye  known  as  Turkey  red  on  cottons.  This  kind  of  dyeing  is 
especially  distinguished  from  others  by  the  fact  that  oil  must 
be  added  to  the  mordants  that  are  to  be  employed.  The 
mordanted  fabric  is  dyed  in  a  bath  of  alizarin,  a  dye-stuff  to 
which  we  shall  return  again.  This  process  of  dyeing  has 
been  long  known  in  the  East ;  but  it  has  been  fully  developed 
only  in  Europe,  and  the  cotton  goods  dyed  in  this  manner  in 
Europe  have  overrun  the  East.  Enormous  numbers  of  hand- 
kerchiefs, more  especially,  dyed  in  this  way  are  sent  to  the 
Eastern  markets. 

This  industry  was  naturally  much  menaced  when  a  new 
red  appeared  in  the  year  1884,  called  congo  red,  which  dyed 
cotton  directly.  Suppose  an  Indian  woman  wants  a  red  cloth, 
she  need  only  dissolve  a  little  congo  red  in  water,  soak  the 
piece  of  cotton  in  the  liquid  for  a  short  time,  and  then  draw  it 
out  dyed  red.  This  red  it  is  true  is  not  nearly  so  fast  as 
Turkey  red  ;  but  that  does  not  matter,  as  a  repetition  of  the 
very  simple  process  will  bring  the  cloth  back  again  to  the 
desired  colour.  Colours  which  will  dye  without  the  employ- 
ment of  mordants  are  called  substantive  colours.  Congo  red 
was  the  first  cotton-dyeing  substantive  colour  known  ;  it  has 
been  followed  by  very  many  others  of  all  varieties  of  shades. 

Substances  known  as  diazo  compounds  have  long  played  an 
important  part,  as  intermediate  products,  in  the  chemistry  of 
the  colours  obtained  from  coal  tar.  Compounds  of  this  class 
are  extremely  ready  to  enter  into  chemical  change ;  and 
while  people  were  engaged  in  one  place  in  experimenting 
on  the  applications  of  colours  prepared  by  the  help  of  these 
compounds  rapid  advances  were  being  made  in  other  places. 
Compounds  can  indeed  be  obtained  which  contain  the  diazo 
group  twice,  and  which  must  be  still  more  chemically 
energetic  than  their  analogues  that  are  but  half  as  richly 


ANILINE  COLOURS  153 

endowed  as  they.  Individual  bodies  of  this  kind  have  long 
been  known  to  science,  and  they  have  been  employed  in 
purely  theoretical  investigations.  The  examination  of  those 
substances  that  bear  the  class  names  bisdiazo,  and  tetrazo, 
compounds  for  the  purpose  of  finding  whether  they  were 
capable  of  technical  applications,  led  to  the  discovery  of  those 
colouring  matters  that  dye  cotton  directly. 

Lack  of  preliminary  knowledge  makes  it  impossible  for  us 
to  go  deeply  into  the  consideration  of  the  coal  tar  colours,  or, 
as  they  are  generally  called,  the  aniline  colours.  Indeed  this 
lecture  will  be  fully  understood  only  by  those  who  have 
a  wide  and  full  chemical  knowledge.  It  should  be  stated 
clearly  that  these  colours  are  not  coal  tar  colours  in  the 
sense  wherein  this  term  is  generally  used  by  the  public.  Tar, 
that  thick,  black  mass,  cannot  be  worked  up  directly  into 
colours. 

The  coal  tar  is  first  of  all  distilled  ;  for  this  purpose  we 
may  employ  an  apparatus  like  that  we  made  use  of  in 
distilling  wine  (see  p.  25).  When  the  tar  is  heated  in  such 
an  apparatus,  clear  water-like  oils  pass  over  for  some  time, 
just  as  spirit  distilled  over  from  the  wine.  These  oils  form  a 
part  of  the  material  from  which  coal  tar  colours  are  manu- 
factured ;  after  these  oils,  distillates  come  over  which  partially 
solidify  on  cooling.  Carbolic  acid  is  obtained  from  these,  and 
later  on  also  naphthalene  and  many  other  bodies,  among  which 
we  need  mention  only  anthracene,  as  that  is  a  substance  we 
shall  have  to  speak  of  again.  If  the  process  of  distillation 
has  been  carried  on  long  enough  a  solid  mass  resembling 
coke,  which  can  be  used  for  burning,  remains  in  the  dis- 
tilling vessel. 

Before  considering  alizarin,  which  is  the  most  important 
colouring  matter  derived  from  anthracene,  we  must  speak  of 


154  CHEMISTRY  IN   DAILY  LIFE 

indigo.  This  blue  dye  has  been  known  from  the  remotest 
times,  and  has  been  made  from  the  juices  of  several  nearly 
allied  plants  which  grow  in  India ;  the  juice  is  itself  colour- 
less, but  when  it  stands  in  the  air  a  process  of  oxidation 
occurs  and  indigo  separates.  As  indigo  is  a  beautiful  blue 
colour,  and  as  it  resists  the  action  of  light  and  air,  of  acids 
and  alkalis,  and  of  substances  used  in  washing,  it  may  well  be 
called  the  king  of  colours. 

There  is  a  European  plant  called  woad>  from  whose  juice 
indigo  separates  on  standing  ;  but  the  quantity  of  indigo  so 
obtained  is  only  about  three-tenths  of  a  per  cent.,  which 
is  very  much  less  than  the  amount  obtainable  from  the  Indian 
plants.  In  olden  times,  however,  because  of  the  slight  con- 
nection between  Europe  and  the  East,  woad  was  used 
exclusively  in  Europe ;  and  as  there  was  a  very  considerable 
demand  for  blue  dyes  the  trade  in  woad-blue  reached  con- 
siderable dimensions  in  some  districts,  and  led  to  the  amassing 
of  large  fortunes. 

In  the  year  1300  there  was  a  large  trade  in  the  neighbour- 
hood of  Erfurt,  where  those  burghers  who  alone  had  the  right 
to  grow  woad  were  known  as  woad  burghers.  Even  as  late 
as  1600  several  hundred  villages  in  Thuringia  were  occupied 
in  the  cultivation  of  woad.  But  at  last  the  trade  could  not 
compete  with  that  in  the  cheaper  Indian  indigo,  although 
both  Princes  and  States  attempted  to  save  it,  not  only 
by  imposing  protective  duties,  but  also  by  prohibiting  the 
importation  of  indigo.  The  Niirnbergers,  for  instance,  were 
long  accustomed  to  swear  to  their  fellow-townsmen  every 
year  that  no  foreign  indigo  would  be  used  in  their  manu- 
factures. Until  recently  Indian  indigo  controlled  the  markets 
of  the  world  ;  but  it  will  not  continue  to  do  this  much  longer. 
In  the  first  place  blue  dye-stuffs  have  been  prepared  from  tar 
which  are  able  to  compete  with  indigo  ;  and  in  the  second 


INDIGO  155 

place  the  problem  of  the  artificial  preparation  of  indigo  was 
completely  solved  in  1880  by  a  series  of  wonderfully  pene- 
trating researches  by  von  Baeyer.  The  preparation  of  indigo 
by  these  methods,  starting  from  coal  tar,  at  present,  however, 
costs  more  than  the  price  of  the  natural  substance.  But 
many  other  methods  have  already  been  worked  out  for  the 
synthesis,  that  is,  the  artificial  production,  of  indigo  ;  and,  as 
a  result  of  work  which  had  been  going  on  for  seventeen  years 
artificial  indigo  was  placed  on  the  market  in  October,  1897,  at 
a  moderate  price.  The  peasants  of  far  Bengal  must  use  their 
fields  for  the  cultivation  of  other  plants.  In  1897  there  were 
500,614  acres  devoted  to  the  cultivation  of  the  plants  which 
yield  indigo  ;  in  1901  the  acreage  was  160,890.  Whereas 
India  produced  about  3j  million  pounds'  worth  of  indigo  in 
1894,  the  value  of  the  indigo  produced  in  1904  was  about 
£500,000.  The  quantity  of  artificial  indigo  used  by  the 
world  to-day  amounts  to  about  85  per  cent,  of  the  total 
consumption. 

As  regards  indigo,  although  on  the  one  hand  it  is  true  that 
the  improved  relations  of  trade  between  India  and  Europe 
have  driven  out  of  cultivation  in  this  part  of  the  world  a 
European  plant  which  yields  a  dye,  yet  on  the  other  hand  we 
know  that  the  advances  made  by  chemistry  in  the  production 
of  dyes  in  the  laboratory,  and  in  connection  therewith  in 
factories  also,  during  the  last  fifty  years,  have  made  the 
cultivation  of  another  similar  plant  unprofitable  in  any  part  of 
the  world. 

This  has  been  the  case  with  madder,  with  which  very 
different  colours,  but  more  especially  a  very  beautiful  red, 
can  be  dyed.  This  plant  was  cultivated  throughout  the 
whole  of  Southern  Europe  as  far  north  as  Baden,  and  also 
in  Asia  Minor,  and  in  other  places.  The  roots  of  this 
plant  were  used  in  dyeing,  and  these  were  known  in  the 


156  CHEMISTRY  IN   DAILY  LIFE 

East  by  the  name   alizari^  from   which   our   word   alizarin 
is  derived. 

-•  These  roots  contain  a  number  of  dye-stuffs.  Although 
very  painstaking  investigations  into  the  chemical  nature  of 
these  substances  had  been  in  progress  since  about  1823,  the 
difficulties  of  the  inquiry  proved  so  great  that  but  little 
advance  was  made  for  many  years.  It  was  not  till  the  year 
1868  that  the  connection  was  established  between  alizarin, 
which  is  the  chief  dye-stuff  in  madder  roots,  and  the  hydro- 
carbon anthracene  which  is  contained  in  coal  tar.  At  a  later 
time  alizarin  was  shown  to  be  chemically  a  dioxyanthraquinone ; 
and  this  knowledge  led  to  a  method  for  converting  anthra- 
cene into  this  dioxyanthraquinone.  At  once  all  the  energies 
of  the  trade  were  devoted  to  the  preparation  of  this  dye-stuff. 
The  methods  that  were  at  first  made  use  of  in  the  laboratory 
were  found  to  be  unsuitable  on  the  large  scale,  hence  these 
methods  had  to  be  replaced  by  others  ;  but,  after  the  ex- 
penditure of  much  labour,  the  manufacture  of  artificial  alizarin 
has  at  last  become  so  perfect  that  it  can  hardly  be  improved 
upon,  and  the  natural  product  is  no  longer  able  to  compete 
with  the  artificial  substance  in  the  matter  of  cheapness.  As 
a  consequence  of  this,  madder  is  no  longer  cultivated  in  any 
part  of  the  world. 

It  has  already  been  mentioned  that  a  series  of  colours  can 
be  obtained  in  dyeing  with  madder,  and  also  with  alizarin  ; 
the  final  colour  depends  on  the  mordant  that  is  used. 
Alumina  mordants  produce  red  dyes  ;  iron  mordants  give 
dark  tones,  passing  into  black  when  much  iron  is  used  ; 
chrome  mordants  dye  violet,  and  so  on.  Very  remarkable 
results  can  be  obtained  by  the  use  of  alizarin.  If,  for 
instance,  a  piece  of  cotton  goods  is  soaked  in  different 
mordants  successively,  hardly  any  change  is  made  in  the 
appearance  of  the  cotton  when  it  is  dried.  But  if  the  material 


ALIZARIN  157 

is  now  dipped  into  boiling  water  wherein  a  little  artificial 
alizarin — which  is  a  yellowish  paste — has  been  dissolved,  and, 
after  remaining  there  for  a  little  time,  it  is  then  washed 
in  much  water,  the  cloth  shows  a  complete  scale  of 
colours. 

Alizarin  comes  into  commerce  in  the  form  of  a  paste 
which  contains  a  large  quantity  of  water,  because  dried  alizarin 
is  but  slowly  dissolved  by  water. 

We  have  still  to  mention  the  extracts  from  woods  that 
have  been  introduced  in  recent  times  into  the  dyeing 
industries.  Aqueous  extracts  of  various  woods,  such  as  log- 
wood or  Brazilwood,  produce  colours  on  mordanted  fabrics 
and  are  therefore  useful  for  dyeing  purposes.  In  order  to 
save  cost  of  transport  these  aqueous  extracts  are  generally 
concentrated  by  evaporation  (in  the  same  way  as  was 
described  under  tanning  extracts,  p.  139)  at  the  seaport 
towns,  and  the  dyer  uses  the  concentrated  extracts  thus 
prepared. 

The  coal  tar  colours  are  dangerous  competitors  against 
these  extracts,  and  it  is  not  unlikely  that  they  may  drive  the 
extracts  out  of  the  field.  At  the  present  time  more  than 
four  hundred  different  coal  tar  colours  are  used  in  dyeing, 
and  the  most  varying  shades  of  colour  are  obtained  from 
these  by  using  different  mordants.  But  that  number  is  very 
small  compared  with  the  vast  array  of  colours  of  this  kind 
that  has  been  prepared.  But  the  demands  for  fastness  in 
colours,  as  regards  the  action  of  light  and  washing,  have 
become  so  much  more  stringent  of  late  years  that  it  is  only 
those  colours  which  completely  satisfy  these  demands  that 
have  any  chance  of  finding  technical  applications. 

Finally  a  word  must  be  said  regarding  dyeing  goods  in 
designs.  The  custom  used  to  be  to  imprint  the  designs 
directly  on  the  goods.  Then  the  method  was  discovered  of 


I $8  CHEMISTRY  IN   DAILY  LIFE 

covering  the  parts  which  it  was  desired  should  remain  undyed 
with  some  substance  that  was  not  permeable  by  the  dyeing 
solution.  Such  a  substance  was  generally  prepared  by  melting 
together  resin  and  wax ;  when  patterns  had  been  stamped  on 
the  cloth  with  this  material  the  whole  was  dipped  into  the 
dyeing  bath,  and  the  goods  came  out  showing  white  patterns 
on  a  coloured  ground.  This  was  followed  by  the  method  of 
printing  the  patterns  ;  the  designs  were  cut  in  wood,  the 
wood  was  covered  with  the  colouring  matter  by  the  use  of  a 
cloth  on  which  the  colour  was  spread,  and  the  wood  was  then 
pressed  down  upon  the  goods.  The  method  was  practically 
the  same  as  that  used  in  everyday  life  for  imprinting  a  name 
cut  in  a  stamp  (which  is  nowadays  generally  made  of  caout- 
chouc) on  to  paper. 

Calico  printing  has,  however,  for  many  years  made  use  of 
machines,  which  have  now  been  brought  to  great  perfection. 
There  are  automatic  machines  in  use  to-day  which  are  able 
to  imprint  sixteen  different  colours  in  succession  on  the  same 
fabric. 


LECTURE   VIII 

Oil-painting — Drying  and  non-drying  oils — Linseed  oil — Varnishes — Inks 
—Cellulose— Paper— Sizing  paper— Straw  boiling— Esparto  grass 
boiling — Soda  cellulose — Sulphite  cellulose — Silvalin. 

THE  process  of  printing  designs  on  goods,  which  we  spoke  of 
at  the  close  of  the  last  lecture,  leads  us  to  consider  painting 
itself,  wherein  prepared  colours  are  mixed  with  such  a  vehicle 
as  size  and  are  then  laid  on  to  the  surfaces  that  are  to  be 
coloured. 

What  are  called  water  colours  are  fairly  satisfactory ;  but 
they  leave  much  to  be  desired,  especially  because  they  can- 
not be  used  in  the  open  air,  as  if  they  get  wet  the  colours 
run. 

In  the  last  few  years  the  easily  prepared  aniline  colours 
have  been  used  in  painting,  whether  with  water  colours  or 
in  oils,  whereas  formerly  only  mineral  colours  were  em- 
ployed. 

These  colours  are  affixed  to  a  basis  of  some  kind  by  the 
help  of  an  oil.  Suppose,  for  instance,  that  a  brick  has  been 
ground  to  very  fine  powder  ;  this  powder  will  represent  an 
almost  indestructible  red  colouring  material.  No  one  would 
use  this  particular  colouring  matter,  because  it  is  not  sufficiently 
beautiful  ;  but  coloured  materials  are  found  in  nature,  or  are 
prepared  by  strongly  heating  or  melting  different  substances, 

159 


160  CHEMISTRY  IN   DAILY  LIFE 

which  can  be  made  ready  for  use  in  painting  by  grinding  in  the 
same  way  as  was  done  with  the  brick.  If,  for  instance, 
cobalt  compounds  are  added  to  glass  during  the  manufacture, 
and  the  resultant  blue  mass  is  finely  ground,  the  extremely 
stable  colouring  material  called  smalt  is  obtained.  Again, 
many  of  the  precipitates  that  are  formed  when  solutions  of 
two  salts  are  mixed  are  available  as  colours  ;  yellow  chromate 
of  lead,  for  instance,  which  is  used  under  the  name  of  chrome 
yellow^  is  prepared  by  mixing  solutions  of  chromate  of  potash 
and  acetate  of  lead. 

The  following  points  are  to  be  noted  in  connection  with  oil 
painting.  Oil  colours  cannot  be  prepared  with  all  kinds  of 
oil.  If  the  colours  were  rubbed  up  with  olive  oil,  for  instance, 
the  products  would  not  dry,  as  olive  oil  leaves  what  are 
called  fat  spots — that  is,  spots  which  never  completely  dry 
up. 

The  oils  fall  into  two  main  classes — drying  and  non-drying 
oils. 

The  chief  constituents  of  the  non-drying  oils,  including 
olive  oil,  are  two  substances  about  which  we  already  know 
something  (see  p.  19) — namely,  oleic  acid  and  glycerin;  and 
this  oleic  acid  is  identical  with  that  which  enters  into  the 
composition  of  such  animal  fats  as  ox  tallow.  In  the  drying 
oils  oleic  acid  is  replaced  by  other  acids  the  names  of  which 
are  generally  derived  from  the  names  of  the  oils  in  which  they 
occur  ;  linseed  oil,  for  instance,  which  is  one  of  the  drying 
oils,  contains  linoleic  acid.  Linseed  oil  is  obtained  by  pressing 
linseed.  We  know  that  seeds  contain  large  quantities  of  oil 
(cf.  p.  60) ;  linseed  [seed  of  the  common  flax]  is  especially 
rich  in  oil,  about  22  per  cent,  of  oil  being  obtained  when  the 
seeds  are  pressed  cold,  and  about  28  per  cent,  when  they  are 
pressed  hot. 


DRYING  OILS  l6l 

Neither  kind  of  oil  can  be  kept  for  a  long  time  in  the  air 
without  undergoing  change.  Olive  oil  and  similar  oils 
become  rancid,  and  the  drying  oils  change  into  hard,  trans- 
parent masses,  especially  if  they  are  spread  out  in  thin  films. 
When  an  oil  becomes  rancid  there  is  a  partial  decomposition 
into  free  fatty  acids  and  glycerin  ;  these  changes  are  thought 
by  some  to  be  brought  about  by  moist  air  alone,  while  others 
suppose  that  the  presence  of  a  bacillus  is  also  necessary.  The 
solidification  of  the  drying  oils  depends  simply  on  a  process 
of  oxidation,  whereby  linoleic  and  similar  acids  are  completely 
changed. 

It  should  be  noted  that  some  oils,  such  as  cotton-seed  oil, 
contain  both  ordinary  oleic  acid  and  another,  drying,  oleic 
acid.  Such  oils  are  distinguished  as  badly  drying  oils,  a 
name  which  explains  itself. 

It  is  a  very  remarkable  fact  that  the  drying  oils  dry 
distinctly  more  rapidly  when  their  oxidation  is  started 
artificially — when  they  are  boiled,  for  instance,  with  a 
substance  such  as  lead  oxide  which  gives  up  oxygen.  Linseed 
oil  which  had  been  boiled  with  lead  oxide  was  used  for 
rubbing  with  colouring  materials  to  form  the  oil  colours  that 
were  used  in  painting  in  the  fourteenth  century. 

Linseed  oil,  the  oxidation  of  which  has  been  started  in 
the  manner  described,  may  be  spread  over  any  selected 
surface,  which  may  or  may  not  have  been  already  treated 
with  water  colours  ;  the  oil  then  dries  to  a  very  hard,  glassy, 
transparent  skin,  and  the  surface  is  said  to  be  varnished. 

The  term  varnish  has,  however,  a  somewhat  wider  significa- 
tion. The  term  is  taken  generally  to  mean,  not  so  much 
boiled  linseed  oil,  as  solutions  of  resins  in  that  oil  or  in  some 
medium  which  readily  evaporates.  Such  solutions  in  very 
volatile  media  are  sometimes  called  lakes  [in  Germany], 
ii 


1 62  CHEMISTRY  IN   DAILY  LIFE 

A  solution  of  shellac  in  alcohol  is  used  as  a  varnish  which 
dries  very  quickly,  as  the  spirit  rapidly  evaporates  when 
exposed  to  the  air.  Spirit  varnishes  are,  however,  looked  on 
with  less  favour  than  solutions  of  resins  in  turpentine  oil, 
because  the  thin  coatings  which  remain  when  the  latter 
evaporate  are  much  firmer  than  those  left  by  spirit  varnishes. 

The  most  lasting  varnishes  are  obtained  by  dissolving 
amber  or  copal  in  boiled  linseed  oil.  Amber,  which  is  a  fossil 
resin,  must  be  melted  before  being  dissolved,  as  raw  amber  is 
insoluble  in  boiled  linseed  oil.  Copal  is  also  a  resin.  Many 
plants  contain  characteristic  liquids  which  flow  from  the 
plants,  either  spontaneously  or  when  the  plants  are  cut,  and 
become  solid  on  standing  in  the  air  ;  these  solidified  masses 
are  called  resins.  The  copal  of  commerce  is  obtained  from  a 
great  many  different  trees  that  grow  in  hot  climates.  Small 
quantities  of  it  are  also  dug  from  the  ground  on  the  east  coast 
of  Africa ;  some  say  that  this  copal  is  a  fossil,  others  that 
it  has  exuded  from  the  roots  of  plants. 

Linoleum  is  made  by  boiling  oxidised  linseed  oil  with 
finely  ground  cork,  and  spreading  the  mixture  on  linen. 

We  must  now  consider  that  coloured  fluid  which  is  used 
more  frequently  than  any  other,  namely,  ink.  (The  name 
is  derived  from  the  Latin  tinctum  =  coloured.)  The  old- 
fashioned  black  ink  is  a  compound  called  gallotannate  of  iron 
suspended  in  water.  It  is  prepared  by  adding  a  solution 
of  sulphate  of  iron  to  an  aqueous  decoction  of  galls.  A  little 
gum  solution  is  always  added,  to  make  the  ink  of  a  better 
consistence  for  writing,  and  also  to  secure  the  more  complete 
suspension  of  the  black  precipitate. 

The  manufacture  of  inks  has  been  made  much  easier 
by  the  discovery  of  aniline  colours  that  are  soluble  in  water. 
Black  ink  is  obtained  by  dissolving  aniline  black  or  indulin 


INK— SYMPATHETIC  INK  163 

black  in  water.  A  solution  of  fuchsin  forms  a  red  ink,  and 
a  more  beautiful  red  ink  is  obtained  by  dissolving  eosin  (770)9 
=  the  morn)  in  water.  Ink  for  manifold  writing  is  prepared 
by  dissolving  I  part  aniline  violet  in  300  parts  of  water,  and 
adding  gum  solution,  etc.  Copying  inks  differ  from  ordinary 
inks  only  in  that  the  former  contain  more  gum  and  also 
some  sugar  ;  so  much  of  the  ink  then  adheres  to  the  paper 
which  is  written  upon  that  a  readable  impression  of  the 
writing  can  be  obtained  in  the  copying  press. 

We  shall  mention  here  the  so-called  sympathetic  inks, 
although  these  play  a  more  important  part  in  exciting 
the  fancy  in  romances  than  in  real  life.  If  characters  are 
written  on  paper  with  a  dilute  solution  of  yellow  prussiate  of 
potash,  nothing  is  to  be  seen  when  the  writing  becomes  dry, 
because  the  salt  has  only  a  very  slight  yellow  colour  ;  but  if  a 
person  who  is  in  the  secret  brushes  the  pages  over  with 
a  pencil  dipped  in  a  dilute  solution  of  chloride  of  iron 
the  writing  stands  out  vividly  in  blue  letters,  because  the  two 
substances  have  reacted  to  produce  Prussian  blue  (see  p.  149). 
It  is  possible  in  this  way  to  cause  writing  to  appear  in  almost 
any  colour  by  a  proper  choice  of  two  liquids  which  react 
together  to  produce  dark  coloured  precipitates,  but  either 
of  which  is  colourless  or  nearly  colourless  when  taken 
alone. 

The  true  sympathetic  ink  should,  however,  be  more  secret 
than  this.  In  the  cases  we  have  spoken  of  the  writing 
remains  legible  once  it  has  been  developed,  but  what  is 
desired  is  that  the  writing  should  fade  away  after  it  has  been 
read  by  the  recipient  of  the  letter.  Such  an  ink  is  generally 
made  from  a  solution  of  chloride  of  cobalt  or  of  chloride 
of  copper.  A  solution  of  the  first  of  these  salts  is  almost 
colourless,  and  writing  traced  with  it  is  invisible  on  white 


164  CHEMISTRY  IN   DAILY  LIFE 

paper.  But  if  the  paper  is  warmed  the  compound  gives 
up  water  which  it  has  been  holding  in  chemical  combination, 
the  deep  blue  anhydrous  chloride  of  cobalt  is  produced,  and 
the  writing  is  very  plainly  seen.  The  writing  disappears  again 
as  the  paper  cools,  because  enough  water  is  absorbed  from 
the  moist  air  to  cause  the  re-formation  of  the  colourless 
hydrated  compound.  If  the  writing  is  done  with  a  solution 
of  chloride  of  copper,  which  solution  has  only  a  very  slight 
bluish  colour,  and  the  paper  is  afterwards  warmed,  the  written 
characters  come  out  in  a  yellow-brown  colour,  and  they 
vanish  again  on  cooling  for  the  same  reason  as  holds  good  in 
the  case  of  chloride  of  cobalt. 

We  shall  meet  with  an  insoluble  ink  when  we  are  describing 
the  process  of  photography. 

We  must  now  proceed  to  the  subject  of  paper. 

In  the  oldest  times  the  only  materials  used  for  writing 
on  were  those  furnished  by  nature,  such  as  stones,  pieces 
of  wood,  or  skins ;  but  the  Egyptians  >Very  long  ago  dis- 
covered how  to  prepare  paper  from  the  papyrus  plant.  The 
stalks  of  that  plant  were  cut  into  as  thin  and  wide  leaflets  as 
possible,  and  these  were  placed  side  by  side  ;  a  second  layer 
of  similar  pieces  was  arranged  transversely  over  the  first,  and 
the  whole  was  placed  under  a  press,  where  it  dried  together 
to  a  single  sheet.  This  was  then  rubbed  as  smooth  as 
possible  and  was  ready  for  writing  on. 

Besides  this  writing  material,  parchment  (see  p.  143)  was 
used  by  the  ancients  and  in  the  earlier  Middle  Ages,  until 
what  we  now  call  paper  was  discovered  in  the  eighth  century. 
The  most  ancient  European  documents  written  on  paper  are 
Papal  bulls  of  the  eighth  and  ninth  centuries.  The  paper 
seems  to  have  been  made  by  the  Moors  in  Spain,  as  the  oldest 
deed  written  on  paper  made  from  linen  is  a  treaty  of  peace 


PAPER  165 

between  Castile  and  Arragon.  The  paper  we  use  nowadays 
consists  of  thin  layers  of  very  strongly  felted  vegetable  fibres  ; 
fibres  from  animal  sources  are  not  suited  for  this  manu- 
facture. 

That  paper  might  be  made  cheaply,  it  used  to  be  the 
custom  not  to  make  direct  use  of  the  fibrous  material  as 
it  came  from  the  plants,  but  to  employ  in  the  manufacture 
the  vegetable  fibres  in  the  rags  that  remained  when  linen 
and  cotton  goods  had  become  worn  out  by  use. 

Accurate  investigations  have  shown  that  all  vegetable 
fibres  consist  of  cellulose  and  other  substances  which  sur- 
round, or  incrust,  the  short  fibres  of  the  cellulose. 

Pure  cellulose  is  a  carbohydrate  (see  p.  66) ;  it  consists 
of  six  atoms  of  carbon,  ten  atoms  of  hydrogen,  and  five  atoms 
of  oxygen  [or  a  whole  multiple  of  these  numbers].  The  com- 
position of  cellulose  is  the  same  as  that  of  starch. 

The  manufacture  of  paper  was  originally  conducted  as 
follows. 

Wet  rags  were  allowed  to  semi-putrefy  for  two  or  three 
days,  whereby  the  substances  that  incrust  the  cellulose  were 
so  far  dissolved  that,  when  the  rags  were  boiled  with  water 
and  a  little  lime,  and  were  then  beaten  in  the  presence  of 
much  water,  the  short  fibres  of  the  cellulose  became  sufficiently 
apparent.  The  pulp  that  was  thus  obtained  was  then  thrown 
on  to  a  fine  sieve  which  was  shaken  to  and  fro  by  a  workman. 
The  greater  part  of  the  water  drained  off  through  the  sieve, 
and  there  remained  a  thin  felted  layer  of  cellulose  fibres 
formed  by  the  interweaving  of  the  single  fibres.  This  was  at 
once  removed  by  a  second  workman  to  a  thick  felt,  where  it 
was  covered  with  another  similar  felt ;  and  when  a  sufficiently 
thick  pile  had  been  built  up,  the  whole  was  placed  under  a 
press,  in  order  to  remove  as  much  water  as  possible,  and 


1 66  CHEMISTRY   IN    DAILY   LIFE 

at  the  same  time  to  give  solidity  to  the  individual  sheets  of 
paper.  The  sheets  were  then  taken  out  of  the  felts  and  were 
thoroughly  dried. 

Paper  made  in  this  way  has  a  loose  texture  like  blotting 
paper.  It  can  be  used  for  printing  on  or  as  packing  paper  ; 
but  it  is  not  suitable  for  writing  on,  because  the  ink  is 
absorbed  and  spread  by  the  little  fibres,  and  the  writing  runs. 
Paper  made  in  this  way  is  also  not  at  all  durable. 

In  order  to  give  greater  consistency  to  such  paper,  and 
also  to  fill  up  its  pores,  it  is  submitted  to  an  operation  called 
sizing^  a  term  which  does  not  accurately  express  the  opera- 
tion in  question.  For  if  size  were  added  alone  to  a  paper 
pulp  containing  much  water,  most  of  the  size  would  go  into 
solution,  and  would  pass  through  the  sieve,  and  only  an 
insignificant  residue  would  remain  in  the  finished  paper.  But 
if  alum  is  added  besides  size  to  the  paper  pulp  a  different 
result  is  obtained.  In  considering  both  tanning  and  dyeing 
we  have  learned  to  recognise  the  great  affinity  that  alum  has 
for  fibres.  Here  also  the  same  cause  is  at  work  ;  the  fibres  of 
the  paper  hold  the  alumina,  and  that  in  turn  prevents  the 
removal  of  the  sizing  material.  When  both  alum  and  size 
have  been  added  to  the  paper  pulp,  then  the  washing  in 
the  sieve  does  not  remove  the  size,  as  it  is  held  in  the  fibres 
of  the  pulp  by  the  alumina.  When  the  paper  is  now  dried 
the  fibres  adhere  together,  and  a  paper  is  produced  which  can 
be  written  on,  as  the  fibres  have  lost  their  capillarity  ;  the  size 
in  the  paper  being  insoluble  in  water  also  makes  the  paper 
less  sensitive  to  the  action  of  moisture. 

The  surface  of  paper  prepared  by  hand  on  a  sieve  cannot 
be  very  smooth ;  hence  all  hand-made  paper  must  be  glazed 
after  it  is  made,  in  order  to  give  it  a  good  appearance.  For 
this  purpose  the  paper  is  either  pressed  when  moist  between 
flat  surfaces,  or  it  is  glazed  by  passing  between  two  highly 


PAPER  167 

polished  rollers  whereby  it  acquires  a  perfectly  smooth  surface. 
Hand  work  in  paper  making  has  been  gradually  and  com- 
pletely replaced  by  machines ;  and  while  formerly  the  single 
sheets  could  not  be  larger  than  the  largest  sieve  that  a  single 
workman  was  able  to  manipulate,  the  machines  produce 
sheets  of  very  considerable  width  and  of  any  length  that 
may  be  desired. 

In  making  paper  pulp  from  rags  it  is  not  now  the  custom 
to  beat  the  rags  after  a  slight  putrefactive  change  has  taken 
place  in  them.  The  rags  are  nowadays  prepared  as  far  as 
possible  for  disintegration  by  boiling  with  a  strong  alkali — 
caustic  soda,  with  which  we  shall  become  better  acquainted 
when  we  come  to  the  soda  industry,  is  used ;  they  are  then 
placed  in  a  rectangular  vessel  in  which  revolves  a  roller  set 
with  knives  which  pass  near  stationary  knives  fixed  in  the 
sides  of  the  vessel.  '  Such  an  apparatus,  called  a  "  breaker," 
with  its  rollers  driven  by  mechanical  energy,  reduces  the 
rags  to  a  state  of  a  fine  division,  and  grinds  them  up  with 
water  to  a  pulp. 

This  pulp  is  then  bleached  by  chloride  of  lime,  and  the 
harmful  after-effects  of  the  bleaching  material  are  neutralised 
by  the  use  of  an  antichlor  (see  p.  146).  The  next  thing  to 
be  done  is  the  sizing.  Glue  is  not  now  used  for  sizing 
machine-made  paper  ;  but  suitable  resins  (which  are  much 
cheaper) — colophony  resins,  for  instance — are  boiled  with 
caustic  soda  lye,  and  the  soaps  thus  produced  (see  soap  in  the 
next  lecture)  are  added,  along  with  alum,  to  the  pulp.  The 
alumina  of  the  alum  being  held  by  the  cellulose,  fixes  the  con- 
stituents of  the  resins,  and  these  bind  together  the  fibres  in 
the  paper,  and  so  make  it  suitable  for  writing  on. 

The  pulp  which  is  now  ready  for  making  into  paper  is 
caused  to  flow  on  to  an  endless  wire  cloth,  made  of  fine  brass 


r~ 


168  CHEMISTRY   IN   DAILY   LIFE 

wire,  care  being  taken  to  dilute  the  pulp  to  the  proper 
consistency  by  a  plentiful  supply  of  water  ;  the  wire  cloth 
is  caused  to  travel  constantly  in  one  direction  by  means  of 
rollers.  A  vibratory  motion  is  at  the  same  time  communicated 
to  the  wire  cloth,  for  the  purpose  of  aiding  the  felting  of  the 
short  fibres  of  the  pulp  ;  and  any  design  that  may  be  woven 
into  the  wire  cloth  appears  as  a  water-mark  in  the  finished 
paper.  The  paper  pulp  from  which  most  of  the  water  has 
already  drained  off  is  now  seized  by  an  endless  felt  which 
carries  the  pulp  with  it ;  a  second  travelling  felt  soon  meets 
the  first,  and  the  pulp  is  pressed  between  these  by  a  pair 
of  rollers,  and  is  thus  nearly  dried.  The  pulp  now  passes  on 
to  a  polished  cylinder  which  is  kept  hot  so  that  the  paper  is 
dried  and  at  the  same  time  receives  a  perfectly  smooth 
surface  ;  a  second  cylinder  serves  to  impart  an  equally  glossy 
appearance  to  the  other  side  of  the  paper.  Finally  the 
machine  makes  up  the  finished  paper  into  rolls. 

It  has  been  found  impossible  for  many  years  to  manufacture 
from  rags  alone  sufficient  paper  to  meet  the  enormous  demand. 
A  consideration  of  the  great  number  of  newspapers  published 
in  these  days  shows  how  impossible  it  would  be  to  make 
paper  enough  from  that  single  source  ;  and  it  must  be 
remembered  that  much  less  waste  linen  or  cotton  is  obtained 
from  each  individual  than  corresponds  to  the  consumption  of 
cellulose  per  head,  be  it  for  writing  paper  or  paper  for  printing 
newspapers  on.  The  paper-making  industry  has  been  growing 
of  late  years  more  rapidly  than  any  other  large  industry. 
As  early  as  the  eighteenth  century  export  duties  were  levied 
on  rags  in  many  countries — in  Prussia,  for  example — in  order 
to  make  it  easier  for  the  home  factories  to  obtain  supplies  of 
this  material.  But  a  measure  of  that  kind  was  not  of  itself 
sufficient  to  cause  an  increase  in  the  supply  ;  and  so  the. 


PAPER   MADE   FROM   WOOD  169 

paper-makers  began  to  look  about  eagerly  for  a  suitable  sub- 
stitute for  rags.  The  result  has  been  that  the  great  advances 
made  in  chemical  knowledge  enable  many  paper  factories  to 
be  carried  on  to-day  without  using  any  rags  at  all. 

A  little  consideration  shows  that  it  is  very  likely  that 
cellulose  should  be  found  in  many  other  plants  besides  in 
that  from  which  linen  is  made.  But  it  is  possible  that 
although  the  chemical  composition  of  cellulose  from  different 
sources  may  be  the  same,  nevertheless  the  physical  properties 
of  the  celluloses  may  differ  (cf.  what  was  said  about  starches 
on  p.  67).  When  straw  is  properly  treated  it  yields  a 
cellulose  ;  and  a  very  convenient  form  of  cellulose  is  obtained 
from  esparto  grass,  which  is  a  plant  that  grows  wild  in  North 
Africa,  especially  in  Algiers. 

It  is  to  be  noted  that  although  every  tree,  and  therefore 
every  kind  of  wood,  must  contain  cellulose,  nevertheless  the 
attempts  that  were  made  to  manufacture  paper  from  wood 
were  not  very  successful  until  recently.  It  happens  that  wood 
was  the  substance  tried  in  the  earliest  attempts  to  find  a 
substitute  for  rags. 

As  far  back  as  1765,  Pastor  Scheffer  of  Ratisbon  proposed 
to  use  macerated  wood  for  making  paper.  The  observation 
of  the  nests  of  wasps  led  him  to  suggest  the  substitution  of 
wood  fibres  for  rag  fibres.  But  the  realisation  of  this  idea 
was  not  accomplished  until  1846,  in  which  year  a  process  of 
wood  grinding  was  introduced  in  South  Germany.  The 
method  is  very  simple  ;  selected  logs  are  held  against  a  wet 
millstone  until  they  are  ground  to  powder.  The  pulp  that  is 
obtained  in  this  way  has  not,  of  course,  exactly  a  fibrous 
structure ;  its  readiness  to  be  felted  is  very  small.  And 
besides  this,  it  is  full  of  resins  from  the  trees  from  which  it 
has  been  made,  and  this  makes  the  bleaching  of  it  very 


I/O  CHEMISTRY  IN   DAILY  LIFE 

difficult  if  not  impossible.  This  wood  pulp  can  only  be 
worked  up  with  rags,  the  longer  fibres  of  which  give  the 
needful  tenacity  to  the  paper,  while  the  wood  pulp  increases 
the  weight.  This  substance  is  indeed  rather  a  "loading" 
than  a  substitute  for  rags. 

The  employment  of  such  loading  stuffs  has  been  carried 
much  further.  Gypsum,  and  substances  of  like  nature,  are 
mixed  with  the  paper  pulp  ;  such  substances  cannot,  it  is 
true,  improve  the  felting  of  the  pulp,  but  when  they  are 
deposited  between  the  felted  fibres  of  the  paper  they  add  to 
the  weight,  although  at  the  same  time  they  reduce  the 
strength,  of  the  paper. 

Besides  the  purely  mechanical  process  of  grinding  wood, 
a  method  was  introduced,  almost  at  the  same  time,  into  the 
paper  industry  for  disintegrating  straw  by  boiling  it  with  soda 
lye,  and  so  obtaining  a  product  which,  after  thorough  washing 
with  water,  could  be  at  once  reduced  to  pulp  in  a  "  breaker." 
The  pulp  that  is  thus  obtained  can  be  bleached  by  chloride 
of  lime,  and  it  may  then  be  mixed  freely  with  the  genuine 
cellulose  that  is  used  in  the  paper  factory.  A  pulp  is  obtained 
by  a  similar  method  from  esparto  grass. 

While  the  disintegration,  by  boiling,  of  straw  or  esparto 
grass,  and  like  substances,  is  easily  carried  out,  the  per- 
formance of  the  same  process  with  wood  is  much  more 
difficult,  because  we  are  dealing  with  a  vastly  more  solid 
material.  The  process  at  first  adopted  as  the  most  con- 
venient was  what  is  known  as  the  soda  cellulose  treatment. 
This  process,  introduced  by  an  American  named  Watt  in 
1860,  consisted  in  boiling  wood,  chiefly  fir  and  pine  wood, 
with  soda  lye  under  a  greatly  increased  pressure.  The 
vessels  were  placed,  like  steam  boilers,  directly  over  the  fire. 
The  raw  material  was  cut  in  thin  shavings  perpendicularly  to 


SULPHITE  CELLULOSE  IJl 

the  stem,  and  these  were  placed,  in  wire  supports,  in  the 
vessels  into  which  the  lye  was  then  run.  The  pressure  must 
be  raised  to  about  ten  atmospheres,  in  order  to  effect  the 
complete  breaking  up  of  the  wood.  When  the  boiling  was 
finished  the  wood  shavings  appeared  dark  brown.  As  all 
the  substances  that  incrust  and  hold  together  the  cellulose 
in  the  wood  had  by  this  time  become  soluble  in  water,  these 
substances  were  dissolved  and  removed  by  stamping  the 
shavings  in  large  quantities  of  water,  in  a  suitable  apparatus : 
and,  after  washing,  only  the  cellulose  remained.  The  product, 
called  soda  cellulose,  came  into  the  market  with  fairly  long 
fibres,  and  as  it  was  easily  bleached  it  was  used  for  working 
up  with  other  materials  into  paper. 

The  substance  known  as  sulphite  cellulose  has  been  a  keen 
competitor  against  the  soda  cellulose  since  the  year  1884,  and 
has  gradually  superseded  it.  Since  1905  soda  cellulose  has 
almost  ceased  to  be  used. 

It  is  of  course  perfectly  conceivable  that  there  should  be 
other  substances  besides  soda; lye  capable  of  disintegrating 
the  bodies  that  incrust  the  cellulose  in  woods,  without 
exerting- too  much  action  on  the  cellulose  itself.  Many  such 
substances  have  been  discovered  in  the  course  of  time,  but 
the  only  one  that  has  been  found  technically  useful  is  acid 
sulphite  of  lime.  The  name  sulphite  cellulose  is  given  because 
the  reagent  used  in  the  process  is  a  sulphite — that  is,  a  salt 
of  sulphurous  acid. 

The  process  of  making  sulphite  cellulose  was  made 
technically  practicable  by  Mitscherlich  ;  although  experi- 
ments in  the  same  direction  had  been  made  before  him 
by  others,  yet  these  experiments  led  to  no  results.  There  is 
indeed  an  English  patent  dating  from  1866  wherein  the  whole 
process  is  nearly  described,  but  only  nearly,  for  never  did  a 
pound  of  cellulose  made  by  that  patent  come  into  the  market, 


172  CHEMISTRY  IN    DAILY  LIFE 

Nothing  can  be  included  in  a  German  patent  that  has 
been  described  by  any  one,  anywhere,  in  the  same  or  in 
a  very  similar  manner,  until  after  fifty  years  have  elapsed 
since  the  last  publication.  The  conditions  are  therefore  very 
unfavourable  to  the  discoverer.  We  know  from  what  we 
learnt  about  tanning  that  almost  all  woods  contain  tanning 
bodies  ;  these  substances  must  go  into  solution,  along  with 
the  other  non-cellulose  constituents  of  the  wood,  when  wood 
is  disintegrated  to  cellulose  by  boiling.  Hence  these  sub- 
stances must  be  found  at  last  in  the  aqueous  liquid,  provided 
they  are  not  decomposed  by  the  special  process  of  boiling 
that  may  have  been  used.  The  specification  of  the  patent 
therefore  stated  that  a  liquor  could  be  obtained  by  boiling 
wood  with  acid  sulphite  of  lime,  which  liquor  was  serviceable 
for  tanning  purposes,  while  cellulose  was  obtained  as  a  bye- 
product. 

But  now,  what  is  acid  sulphite  of  lime  ? 

We  all  know  that  when  sulphur  is  ignited  it  burns  with  a 
very  penetrating  odour,  and  gradually  disappears,  and  just 
as  carbon  produces  the  gas  carbonic  acid  when  it  burns,  so 
burning  sulphur  forms  sulphurous  acid,  which  is  also  a  gas. 
Acids  combine  with  bases  to  form  salts  (see  p.  49) ;  if,  then, 
the  gas  coming  from  a  furnace  in  which  sulphur  is  burning 
is  led  into  a  chimney  that  is  not  empty  as  chimneys  usually 
are  but  is  filled  with  limestone  which  is  kept  moist,  the 
sulphurous  acid  will  not  escape  into  the  air,  but  will  combine 
with  the  basic  lime  to  form  sulphite  of  lime.  As  there  will 
be  much  sulphurous  acid  gas  at  the  bottom  of  the  chimney, 
and  as  this  gas  is  very  soluble  in  water,  an  acid  solution 
of  the  gas  will  be  produced  at  this  point,  and  the  sulphite  of 
lime  that  is  formed  will  dissolve  in  this  acid  liquor  to  form 
acid  sulphite  of  lime. 


ACID   SULPHITE  OF  LIME  173 

A  solution  of  acid  sulphite  of  lime  attacks  most  metals 
energetically.  Lead  is  the  metal  which  best  withstands  the 
action  of  chemical  reagents,  and  at  the  same  time  is  not  too 
costly  when  it  has  to  be  used  in  considerable  quantities ;  for 
this  reason  leaden  vessels,  or  vessels  covered  with  lead,  are 
very  often  used  in  chemical  industries. 

If  cellulose  is  to  be  prepared  from  wood  by  the  action 
of  the  acid  sulphite  liquor,  the  wood  must  be  boiled  with  the 
liquor  under  a  pressure  of  about  three  atmospheres.  Now 
lead  is  so  soft  that  it  is  impossible  to  make  leaden  vessels 
that  will  withstand  much  pressure ;  hence  it  was  a  very 
difficult  problem  to  construct  vessels  suitable  for  carrying 
out  the  process  of  making  sulphite  cellulose  on  the  large 
scale.  The  following  method  is  now  employed.  An  or- 
dinary boiler  is  lined  inside  with  resin  on  which  are  laid 
plates  of  lead ;  these  plates  are  then  covered  with  acid- 
resisting  flagstones  arranged  in  two  layers  in  such  a  way 
that  the  joints  between  the  upper  and  the  under  layers  are 
separated  from  one  another  by  half  the  breadth  of  one  of 
the  stones.  Several  systems  of  leaden  pipes  are  placed  in 
the  boiler  for  the  purpose  of  heating  it,  and  steam  is  led 
in  through  these  pipes  from  another  boiler.  It  is  necessary 
to  have  several  sets  of  pipes,  because  one  or  other  of  the 
pipes  occasionally  bursts. 

Wood  which  has  been  boiled  with  the  acid  sulphite  of  lime 
liquor  leaves  the  boilers  less  coloured  than  when  it  went  in  ; 
in  this  respect  it  differs  from  wood  boiled  with  soda  lye. 
Remembering  that  sulphurous  acid  is  an  effectual  bleaching 
agent  (see  p.  147)  we  see  that  there  can  be  no  difficulty 
in  turning  out  perfectly  white  cellulose  by  this  process. 

The  best  product  is  obtained  from  the  wood  of  the  silver 
fir.  This  tree  does  not  flourish  farther  north  than  the  Main  ; 
and  as  the  trees  are  most  suited  for  cellulose  making  when 


174  CHEMISTRY   IN   DAILY  LIFE 

they  are  about  fifteen  years  old,  and  the  demand  has  greatly 
increased  of  late  years,  the  planting  of  these  trees  is  a  matter 
to  be  commended  to  the  consideration  of  the  managers  of 
forestry.  Farther  north  much  use  is  made  of  pinewood. 

The  fact  that  a  medium-sized  establishment  for  making 
sulphite  cellulose  consumes  daily  five  or  six  acres  of  well- 
timbered  pine-forest,  gives  us  a  good  notion  of  the  scale  on 
which  the  manufacture  of  this  substance  is  now  carried  on. 

Sulphite  cellulose  has  almost  driven  out  soda  cellulose. 
Not  only  this,  but  sulphite  cellulose  is  taking  the  place  of  the 
raw  material  that  was  formerly  employed  in  paper  making. 
We  have  already  learned  (see  p.  in)  that  spirits  can  be 
made  from  the  liquor  obtained  in  preparing  sulphite  cellu- 
lose. 

Finally  it  should  be  mentioned,  as  showing  the  superiority 
of  the  cellulose  made  by  the  sulphite  process,  that  some  very 
skilful  workers  have  made  attempts  so  to  disintegrate  wood 
by  this  process  that  cellulose  may  be  obtained  in  such 
long  fibres  that  it  may  be  interwoven  with  cotton  and  thus 
serve  as  a  partial  substitute  for  that  material. 

These  attempts,  which  have  been  in  progress  since  1890, 
have  not  led  directly  to  the  desired  result ;  but  fibres  which 
can  be  woven  have  been  obtained  in  the  following  way. 
Paper  made  from  cellulose  is  run  over  ribbed  cylinders,  so 
that  slips,  instead  of  sheets,  of  paper  are  produced,  and  these 
are  converted,  while  moist,  into  threads,  by  twisting,  which 
is  a  kind  of  spinning.  These  paper-threads  are  then  used  as 
the  woof,  and  threads  of  cotton  as  the  warp,  in  weaving  a 
fabric,  70  per  cent,  of  which  consists  of  paper.  The  fabric 
has  been  called  silvalin  (from  the  Latin  silva,  a  wood,  or 
forest).  The  durability  of  silvalin  is  remarkable  ;  sacks 
made  of  it,  and  filled  with  goods,  have  gone  round  the  world 


SILVALIN  175 

and  been  none  the  worse.     It  seems  as  if  silvalin  yarn  would 
become  a  not  inconsiderable  rival  of  jute. 

When  one  considers  that  materials  made  from  wood  by 
chemical  processes  are  constantly  finding  new  applications, 
one  cannot  be  astonished  at  the  great  rise  in  the  price  of 
wood. 


LECTURE   IX 

Burnt  lime— Potash— Soda  by  Leblanc's  process— Sulphuric  acid— Sul- 
phate of  Soda — Nitric  acid — Bleaching  powder — Soda  crystals — 
Ammonia  soda  process — Ashes  of  molasses — Ashes  from  the  wash- 
ings of  wool — Soap — Caustic  alkali — Caustic  soda — Soft  soaps — 
Loaded  soaps— Curd  soaps— Hard  and  soft  waters— Plasters. 

THE  preparation  of  soaps,  which  we  have  now  to  consider, 
is  brought  about  by  the  action  of  caustic  alkalis  on  fats. 
Before  we  are  in  a  position  to  deal  with  soaps  we  must 
consider  in  some  detail  the  caustic  alkalis,  and  also  the 
carbonated  alkalis,  as  the  manufacture  of  one  of  these  cannot 
be  separated  from  that  of  the  other. 

The  burning,  or,  to  speak  more  accurately,  the  intense 
heating,  of  limestone  was  practised  in  ancient  times  ;  and  in 
these  days  burnt  lime  was  the  only  caustic  alkali  known 
throughout  the  world. 

The  following  considerations  explain  why  burnt  lime  has 
been  known  since  ancient  times.  When  stones  are  placed  so 
as  to  form  a  hearth  wherein  a  fire  is  to  be  burned,  most  of 
the  stones  used  for  this  purpose  remain  unchanged  when  the 
fire  has  gone  out.  Only  one  kind  of  stone  is  altogether 
altered  by  the  process.  When  that  stone  has  become  cold, 
the  falling  of  rain  on  it,  or  the  pouring  of  water  upon  it,  causes 
it  to  become  hot  again  ;  the  water  begins  to  pass  off  as 
steam,  and  the  hard  stone  falls  to  powder.  The  stone  which 

176 


SLAKED  LIME  177 

behaves  thus  is  found  abundantly  in  nature.  It  is  called 
limestone  ;  the  purest  forms  of  it  are  called  marble,  calcspar, 
or  chalk.  Burnt  limestone,  or  burnt  lime  as  it  is  generally 
called,  is  used  for  making  mortar,  to  which  we  shall  refer 
hereafter.  With  the  help  of  what  we  have  already  learned, 
we  are  able  to  explain  the  behaviour  of  this  stone,  in  the 
following  way.  Limestone  is  carbonate  of  lime.  When  it  is 
heated,  carbonic  acid  escapes  as  a  gas,  and  lime  *  remains. 
Natural  limestone  is  an  excellent  building  material,  because 
it  is  but  slightly  affected  by  weather-conditions.  Burnt 
limestone,  however,  falls  to  pieces,  slakes  as  it  is  said,  by  the 
action  of  water.  By  reason  of  the  chemical  reaction  between 
burnt  lime  and  water,  so  much  heat  is  produced  that  some  of 
the  water  is  changed  to  steam. 

Slaked  lime  has  very  caustic,  that  is,  destructive,  properties  ; 
hence,  it  is  known  as  caustic  lime.  Inasmuch  as  it  combines 
with  acids  to  form  salts,  it  is  chemically  a  base  or  an  alkali 

(P-  49> 

Although  lime  slakes  with  water,  and  combines  with  some 

of  the  water,  nevertheless  it  is  but  slightly  soluble  in  water. 
Combination  with  water,  and  dissolving  in  water,  are  two 
quite  different  things.  Already  in  the  Middle  Ages,  the 
soap-maker  knew  how  to  use  lime  for  making  an  alkali 
which  is  very  soluble  in  water.  This  substance  was  known  as 
caustic  alkali.  It  is  made  to-day,  as  it  was  made  in  ancient 
times,  from  potashes,  by  using  caustic  lime. 

We  shall  consider  the  process  for  making  caustic  alkali  after 
we  have  made  clear  what  potashes  is  (see  p.  178). 

*  Lime  is  the  oxide  of  a  metal,  calcium  ;  calcium  oxide  eagerly 
combines  with  water.  In  this  combination,  much  heat  is  produced  ; 
the  calcium  oxide  changes  to  calcium  hydroxide,  which  is  known  as 
slaked  lime. 

CaO       +    H20  =        Ca(OH)2. 

Calcium  oxide  +    Water   =    Calcium  hydroxide. 
12 


I?8  CHEMISTRY   IN   DAILY  LIFE 

We  know  (see  p.  37)  that  all  land  plants  must  have  potash 
salts  if  they  are  to  live  ;  every  kind  of  wood,  for  instance, 
contains  potash  salts,  and  when  the  wood  is  burnt  these  salts 
are  found  in  the  ashes.  The  ashes  of  plants  contain  potash 
salts  chiefly  as  carbonate  of  potash,  which  is  a  salt  that  is  very 
soluble  in  water.  If  the  ashes  are  boiled  with  water  in  pots 
the  potash  salts  go  into  solution,  and  when  this  solution  is 
evaporated  these  salts  are  found  in  the  solid  residue,  which  is 
known  as  potashes  (or  pot-ashes). 

Potashes  is  a  substance  that  was,  and  is,  very  much  used  ; 
it  is  employed,  for  instance,  in  making  soap,  in  manufacturing 
glass,  in  dyeing,  etc.  As  forests  were  cut  down  the  supply  of 
potashes  became  less  ;  this  narrowing  of  the  supply  made  itself 
definitely  felt  at  first  in  France,  where,  as  long  ago  as  1775, 
the  Academy  of  Paris  offered  a  prize  of  2,500  livres  (about 
£"5,000),  not  for  a  process  for  making  potashes  artificially, 
but  for  a  method  whereby  common  salt  could  be  converted 
into  soda,  because  soda  could  be  used,  in  most  cases,  as  a 
substitute  for  potash. 

Matters  were  in  this  position.  Potashes  is  carbonate  of 
potash  ;  soda  was  also  known  to  be  a  carbonate.  No  natural 
source  of  potash  was  known  other  than  potashes.  The 
Stassfurt  salt  deposits  (see  p.  46)  were  not  discovered  till  the 
second  half  of  the  nineteenth  century ;  and  there  was  no 
method  known  at  that  time  for  making  potash  from  other 
compounds  of  potash. 

The  only  source  of  soda  salts  available  at  that  time 
was  the  ash  of  sea  plants,  which  plants  contain  soda  (obtained 
by  them  from  the  salt  in  the  sea)  in  place  of  the  potash 
of  land  plants  ;  this  ash  was  prepared  chiefly  in  North  Spain, 
and  was  known  as  barilla.  The  greater  part  of  the  barilla  of 
that  time  consisted  of  impurities  ;  only  about  5  per  cent,  of 
soda  was  present  in  it.  Nevertheless  so  great  was  the  de- 


SODA  MAKING  179 

mand,  or  we  might  say  the  greediness,  for  soda  that  this 
barilla  was  used  in  various  industries.  Now  soda  is  carbonate 
of  'sodium ,  and  it  was  known  even  in  those  days  that  there  is 
a  practically  unlimited  supply  of  sodium  compounds  in 
common  salt,  which  is  composed  of  sodium  and  chlorine. 
And  it  so  was  that  a  prize  was  offered,  in  1775,  for  a 
method  of  making  soda  from  salt,  because  there  seemed  to 
be  no  possibility  of  finding  a  process  for  manufacturing 
potash  salts. 

The  following  figures  give  a  notion  of  the  value  of  soda 
salts.  In  1814  a  ton  of  soda  crystals  cost  about  £6$  ;  in 
1824  the  cost  was  about  £32  ;  and  it  is  now  about  £3. 
The  prices  that  ruled  at  the  time  we  are  speaking  of 
made  possible  a  very  large  profit  on  the  manufacture  of 
soda. 

After  many  unsuccessful  attempts  by  other  people,  the 
problem  was  solved  by  Leblanc,  who  took  out  a  patent  in 
1791. 

Leblanc's  method  was  extremely  complicated.  To  conduct 
the  process  at  all  requires  chemical  knowledge  of  the  most 
varied  kind  ;  and  to  apply  the  improvements  that  have  been 
worked  out  in  the  laboratory,  and  to  carry  into  practice  the 
many  subsidiary  manufactures  that  have  sprung  from  this 
main  industry,  demand  so  much  technical  ability  that  it  may 
be  said  that  this  manufacture  is  not  merely  the  foundation 
of  the  immense  chemical  industries  of  the  present  day,  but  it 
is  also  the  guiding  spirit  in  these  industries.  The  fame  of 
the  Leblanc  process  will  remain  for  all  time. 

Leblanc  did  not,  any  more  than  his  contemporaries,  make  it 
possible  to  change  common  salt — that  is,  chloride  of  sodium 
— directly  into  carbonate  of  soda.  His  discovery  consisted 
in  making  it  possible  to  change  sulphate  of  soda — which  is 


ISO  CHEMISTRY  IN   DAILY  LIFE 

obtained  from  common  salt  without  much  difficulty— into 
carbonate  of  soda. 

Leblanc's  process  consists  of  the  following  parts.  Common 
salt  (chloride  of  sodium)  is  changed  into  sulphate  of  soda  by 
heating  with  sulphuric  acid.  The  sulphate  of  soda  is  then 
mixed  with  coal  and  chalk  (chalk  is  carbonate  of  lime),  and 
the  mixture  is  heated  until  it  melts  ;  the  melted  mass  is 
lixiviated  with  water,  and  the  solution  which  contains  car- 
bonate of  soda  is  evaporated  ;  the  crystals  that  separate  are 
the  soda  crystals  of  commerce. 

The  salt  sulphate  of  soda,  into  which  common  salt  is  con- 
verted in  the  first  stage  of  the  manufacture  of  soda,  is 
ordinarily  known  as  Glauber's  salt,  from  Glauber,  who  first 
prepared  it  in  1645. 

The  manufacture  of  soda  by  the  Leblanc  process  requires 
the  use  of  sulphuric  acid ;  and  the  manufacture  of  this  acid 
is  intimately  bound  up  with  that  of  soda  by  Leblanc's 
method. 

We  know  that  gaseous  sulphurous  acid  is  produced  when 
sulphur  is  burnt  (see  p.  172).  Now  to  convert  sulphurous 
into  sulphuric  acid  an  atom  of  oxygen  must  be  added  to  the 
former.  This  can  scarcely  be  done  directly  ;  but  the  addition 
of  the  oxygen  is  performed  easily  in  presence  of  nitric  acid. 
Experience  has  shown  that  the  process  is  best  conducted  in 
large  chambers,  which  are  made  of  lead  that  they  may  resist 
the  action  of  the  acid  (cf.  p.  173).  The  nitric  acid  loses 
oxygen  which  goes  to  oxidise  the  sulphurous  acid  to  sulphuric 
acid.  As  constant  supplies  of  air  and  water  vapour  are  led 
into  the  chamber,  the  products  of  the  deoxidation  of  the 
nitric  acid  are  constantly  changed  back  into  nitric  acid  ;  the 
nitric  acid  thus  serves  as  a  carrier  of  the  oxygen  of  the  air  to 
the  sulphurous  acid,  and  hence  a  comparatively  small  quantity 


SULPHURIC  ACID  l8l 

of  nitric  acid  is  required.     The  sulphuric  acid  collects  as  a 
liquid  on  the  bottom  of  the  chamber. 

The  manufacture  of  sulphuric  acid  evidently  carries  with  it 
the  making  of  nitric  acid.  That  acid  is  sometimes  called  [aqua 
fortiS)  and  sometimes]  parting  acid,  because  it  is  used  to  part 
gold  and  silver,  only  the  latter  of  these  metals  being  soluble 
in  nitric  acid.  The  acid  is  made  by  the  action  of  sulphuric 
acid  on  saltpetre,  and  soda  saltpetre  is  used  because  of  its 
cheapness  (cf.  Chili  saltpetre  on  p.  50).  The  products  of  the 
reaction  of  these  two  compounds  are  sulphate  of  soda,  and 
nitric  acid  which  is  easily  separated  by  distillation. 

After  about  100  years,  during  which  the  manufacture  of 
sulphuric  acid  by  the  agency  of  nitric  acid  had  been  more 
and  more  improved,  a  serious  competitor  appeared  about  the 
year  1896  in  the  form  of  a  new  method  of  making  the  acid. 
This  method  is  as  follows.  Very  finely  divided  platinum  has 
the  property  of  causing  many  chemical  reactions  to  proceed 
which  do  not  occur  in  the  absence  of  it.  This  behaviour  of 
finely  divided  platinum  reminds  one  slightly  of  that  of  pepsin 
(see  p.  53)  or  of  diastase  (see  p.  100).  Sulphuric  acid  is  pro- 
duced by  bringing  sulphurous  acid  and  air — of  course,  it  is 
only  the  oxygen  of  the  air  that  is  concerned  in  the  process— 
into  contact  with  finely  divided  platinum.  This  reaction, 
which  seems  so  simple  and  has  been  known  in  the  laboratory 
for  a  long  time,  is  so  difficult  to  carry  out  on  the  large  scale 
that  it  is  only  recently  that  all  difficulties  have  been  over- 
come. 

Sulphuric  acid  used  to  be  prepared  in  the  manner  indicated 
above  from  sulphur  ;  but  in  the  year  1838  the  price  of  sulphur 
rose  from  £5  los.  to  £15  per  ton,  because  in  that  year  the 
then  King  of  Naples  leased  to  a  Marseilles  firm  a  monopoly 
for  making  sulphur  in  Sicily,  which  is  the  only  European 
country  where  sulphur  is  found  in  quantity.  The  making  of 


1 82  CHEMISTRY   IN    DAILY   LIFE 

sulphur  began  in  earnest  in  Louisiana  (America)  only  in  1906. 
The  English  sulphuric  acid  factories — and  almost  all  the 
factories  at  that  time  were  in  England — grumbled  exceed- 
ingly, and  a  kind  of  sulphur  war  threatened  to  break  out ;  the 
result  was  that  the  monopoly  was  withdrawn. 

But  meanwhile  necessity  had  led  to  new  inventions.  It  is 
true  that  there  is  not  much  free  sulphur  to  be  found  in 
Europe  ;  but  there  are  numerous  deposits  of  sulphur  com- 
pounds scattered  about  the  world,  especially  deposits  of 
sulphide  of  iron  which  forms  the  mineral  known  as  pyrites. 
Pyrites  can  be  burnt  in  ovens ;  and  under  these  conditions 
the  sulphur  of  the  pyrites — and  pyrites  contains  about  48  per 
cent,  of  sulphur — is  burnt  to  sulphurous  acid,  while  the  iron 
is  burnt  to  oxide  of  iron  which  can  be  used  in  iron  making. 
There  is  also  the  mineral  copper  pyrites^  coming  for  the  most 
part  from  Spain,  which  can  be  used  for  making  sulphuric 
acid  ;  this  mineral  is  willingly  employed  by  the  sulphuric 
acid  maker,  because  the  extraction  of  copper  from  the  burnt 
residue  is  a  paying  business.  Here  is  an  example  of  a 
subsidiary  industry  depending  on  the  Leblanc  soda  industry. 

Sulphuric  acid  is  one  of  those  commercial  articles  which 
are  manufactured  in  enormous  quantities.  Besides  what  is 
required  in  soda  making,  we  have  but  to  think  what  quantities 
of  sulphuric  acid  must  be  used  every  year  in  the  process 
of  decomposing  phosphorite  and  burnt  bones  to  make  them 
into  artificial  manures,  and  how  much  must  be  needed  for 
manufacturing  sulphate  of  ammonia  for  the  use  of  the  farmers 
(cf.  pp.  43  and  50). 

The  quantity  of  sulphuric  acid  manufactured  in  the  world 
in  the  year  1909  amounted  to  about  8,000,000  tons.  Of  this 
quantity,  England  made  about  2,100,000  tons,  Germany 
about  1,385,000  tons,  the  United  States  about  1,300,000  tons, 
and  France  about  800,000  tons.  In  that  year,  about  240 


HYDROCHLORIC   ACID  183 

tons  of  sulphuric  acid  were  made  each  hour  in  England  ;  the 
price  of  a  ton  of  the  acid  was  about  £3  los. 

When  sulphuric  acid  reacts  vith  common  salt  (chloride  of 
sodium)  not  only  is  sulphate  of  sodium  formed,  but  hydro- 
chloric acid  is  also  produced. 

Common  salt  +  sulphuric  acid  =  sulphate  of  soda  +  hydrochloric 

acid. 

Hydrochloric  acid  is  a  gas,  and  like  sulphurous  acid  or 
ammonia  gas  it  is  very  soluble  in  water.  Commercial  hydro- 
chloric acid,  which  is  an  aqueous  solution  of  the  gas,  contains 
about  33  per  cent,  of  the  acid.  This  commercial  acid  is  a 
liquid  which  fumes  slightly  in  the  air ;  when  it  is  evaporated 
the  hydrochloric  acid  gas  that  is  given  off  forms  clouds  with 
the  moisture  of  the  air.  In  the  earlier  days  of  the  soda 
industry  no  use  could  be  found  for  the  hydrochloric  acid 
produced  in  the  manufacture,  and,  as  it  was  allowed  to  escape 
into  the  air  with  the  gases  from  the  furnaces,  it  formed  a 
terrible  nuisance.  All  vegetation  died  in  the  neighbourhood 
of  the  soda  factories,  and  complaints  were  loud  and  deep.  In 
a  suburb  of  Brussels  the  tools  of  the  artisans  living  there 
were  so  corroded  by  the  acid  as  to  become  useless  in  a  short 
time.  An  attempt  was  made  in  one  factory  to  get  rid  of 
the  gas  by  leading  it  up  a  chimney  150  metres  [nearly 
500  feet]  high — that  is,  about  twice  the  height  of  an  ordinary 
church  spire — but  instead  of  mixing  with  the  air  at  the 
top  of  the  chimney,  the  gas  fell,  in  wet  weather,  in  heavy 
clouds  on  to  the  ground  beneath. 

To  stop  the  complaints  some  English  factories  were  put 
out  of  the  way  on  to  small  islands  in  the  canals;  but  although 
the  great  solubility  of  hydrochloric  acid  in  water  was  well 
known,  there  was  no  possibility  of  getting  rid  of  the  acid  by 


1 84  CHEMISTRY   IN    DAILY   LIFE 

this  procedure,  for  the  aqueous  hydrochloric  acid  could  not 
be  run  into  rivers,  as  it  would  kill  the  fish. 

Hydrochloric  acid  remained  for  long  a  veritable  plague 
to  the  manufacturers ;  but  gradually  matters  completely 
changed.  Hydrochloric  acid  found  its  most  important  use 
in  making  chloride  of  lime,  which  was  consumed  in  large 
quantities  for  bleaching  (see  p.  145). 

In  order  to  make  chloride  of  lime  from  hydrochloric  acid 
the  gaseous  acid  is  first  of  all  led  into  water.  The  destructive 
action  of  the  acid  gas  on  the  surroundings  of  the  works  is 
thus  obviated.  The  aqueous  solution  of  the  acid  is  then 
heated  with  pyrolusite,  a  mineral  which  consists  chiefly  of 
peroxide  of  manganese ;  in  this  reaction  between  manganese 
peroxide,  which  is  very  rich  in  oxygen,  and  hydrochloric 
acid,  which  is  a  compound  of  hydrogen  and  chlorine,  the 
oxygen  of  the  manganese  peroxide  combines  with  the 
hydrogen  of  the  acid  to  form  water,  and  chlorine  is  set 
free ;  it  is  then  only  necessary  to  lead  the  chlorine  into 
chambers  wherein  lime  is  spread  in  order  to  form  chloride 
of  lime. 

Manganese  peroxide  -f  hydrochloric  acid  =  manganese  chloride  + 
water  +  chlorine  gas. 

A  very  considerable  amount  of  hydrochloric  acid  is  pur- 
chased by  those  who  conduct  other  chemical  industries  for 
use  in  their  works. 

For  starting  the  first  manufactory  for  carrying  out  his 
process  Leblanc  naturally  required  a  large  sum  of  money. 
The  money  was  furnished  by  the  Duke  of  Orleans,  afterwards 
known  as  Philippe  Egalite,  on  the  strength  of  a  report 
testifying  to  the  soundness  of  the  project  by  d'Arcet,  professor 
of  chemistry  in  the  College  de  France^  at  Paris. 

Egalite's  life  was  brought  to  an  end  in  1793  by  the  guillotine, 


SODA  MAKING  185 

and  the  soda  factory  was  confiscated  along  with  his  other 
possessions.  After  this  the  constant  wars  of  the  Republic, 
by  preventing  the  transport  of  goods  to  the  sea,  caused 
potashes  to  become  very  scarce  in  France,  and  a  decree  was 
issued  by  The  Committee  of  Public  Safety,  commanding  that 
all  the  processes  for  making  soda  that  had  been  discovered 
(see  pp.  178,  179)  should  be  made  known.  In  this  way 
Leblanc's  patent  collapsed.  The  factory  was  restored  to 
Leblanc  in  1799;  DUt  ne  could  not  carry  it  on  for  want 
of  means,  and  in  1806  this  great  inventor  committed  suicide 
in  despair. 

The  process  of  Leblanc  was  not  forgotten,  but  it  dragged 
along  without  much  effect  until  it  was  taken  up  and  developed 
by  some  English  manufacturers.  The  soda  industry  did  not 
grow  much,  however,  in  England  until  after  1824,  in  which 
year  the  duty  of  about  £30  per  ton  was  removed. 

The  soda  manufactured  in  London  must  for  a  time  have 
been  given  away,  in  order  to  accustom  the  soap-makers  to 
the  use  of  soda  and  to  induce  them  to  give  up  the  employ- 
ment of  barilla  (see  p.  178).  But  this  state  of  affairs  was  soon 
changed,  as  it  was  found  that  the  work  of  soap-making  was 
done  much  more  quickly  and  conveniently  by  using  the  pure 
soda  than  when  the  unsatisfactory  barilla  was  employed. 
Indeed  after  a  time  people  were  glad  to  get  hold  of  the 
crude  melted  masses  that  came  from  the  soda  ovens,  and 
to  lixiviate  these  for  themselves,  rather  than  to  use  barilla. 

Soda  had  gained  a  firm  footing.  The  manufacture  of  soda 
by  Leblanc's  process  began  in  Germany  in  1830  at  Schonebeck 
on  the  Elbe. 

To  make  soda  by  the  Leblanc  process  it  is  necessary  to 
lelt  together  Glauber's  salt  (sulphate  of  soda),  chalk,  and 


1 86  CHEMISTRY   IN    DAILY   LIFE 

coal.  The  sodium  that  goes  to  make  the  soda  is  obtained 
from  the  Glauber's  salt,  and  the  carbonic  acid  from  the  chalk, 
which,  as  we  know,  is  carbonate  of  lime.  The  reactions 
that  occur  in  the  process  of  melting  are  so  complicated 
that  it  is  not  possible  for  us  to  go  into  them  in  this  place. 
The  soda  (carbonate  of  sodium)  in  the  melted  product  is 
dissolved  out  by  lixiviating  with  water,  and  this  solution 
is  evaporated  until  less  water  remains  than  suffices  to  keep 
the  soda  in  solution ;  the  soda  crystallises  out  from  this 
liquid  as  it  cools.  The  soda  crystals  that  form  contain 
almost  exactly  63  per  cent,  of  water,  which  is  held  fast  by 
the  crystals  and  is  known  as  water  oj  crystallisation.  Many 
salts  have  this  property  of  binding  to  themselves  definite 
quantities  of  water  of  crystallisation. 

When  soda  crystals  are  exposed  to  the  air  for  a  long  time 
they  undergo  a  visible  change — they  lose  a  part  of  their  water 
of  crystallisation,  and  the  crystals  fall  to  powder,  as  it  is  only 
when  combined  with  the  water  of  crystallisation  that  they 
exhibit  their  characteristic  crystalline  form.  The  large 
amount  of  water  of  crystallisation  in  soda  crystals  would  add 
unnecessarily  to  the  cost  of  carriage,  and  for  this  reason  it  is 
customary  to  manufacture  anhydrous  carbonate  of  soda  by 
strongly  heating  soda  crystals  until  all  the  water  of  crystallisa- 
tion is  removed.  The  product  known  as  calcined  soda  is  sent 
into  the  market  in  the  form  of  a  white  powder. 

We  have  now  become  acquainted  with  the  broad  outlines 
of  the  Leblanc  soda  process,  and  we  have  also  learnt  some- 
thing of  the  chief  of  those  bye-industries  which  have  been 
created  by  this  process.  The  existence  of  this  process,  which 
had  been  carried  on  successfully  for  something  like  sixty 
years,  began  to  be  threatened  about  the  beginning  of  the 
year  1880  ;  and  the  making  of  soda  by  the  Leblanc  method 


AMMONIA   SODA  PROCESS  187 

is  now  virtually  ceased.     How  that  has  come  about  is  now 

be  described. 

A  much  simpler  method  for  transforming  common  salt 
ito  soda  than  that  used  in  the  Leblanc  process  has  been 
known  for  a  long  time.  The  principle  of  this  method,  which 
in  easily  be  carried  out  in  the  laboratory,  is  as  follows. 
The  base  ammonia  combines  with  a  certain  quantity  of 
carbonic  acid  to  produce  carbonate  of  ammonium,  and  it 
also  combines  with  twice  as  much  carbonic  acid  to  form 
bicarbonate  of  ammonium ;  when  a  solution  of  the  last- 
named  salt  is  added  to  a  solution  of  common  salt  double 
decomposition  occurs,  and  a  precipitate  of  the  comparatively 
insoluble  bicarbonate  of  soda  is  produced,  while  salammoniac 
(chloride  of  ammonium)  remains  in  solution. 

Bicarbonate  of  ammonium  +  sodium  chloride  == 

(soluble  in  water)  (soluble  in  water) 

bicarbonate  of  soda  +  chloride  of  ammonium. 

(only  slightly  soluble  in  (soluble  in  water  ;  remains 

water,  therefore  precipitates)  in  solution) 

By  this  reaction  common  salt  is  changed  directly  into 
bicarbonate  of  soda. 

The  process  based  on  this  reaction  is  theoretically  extremely 
simple.  The  first  patent  dates  from  1838;  and  we  know 
that  soda  was  made  by  this  process  in  the  years  1854-57 
in  a  French  factory,  and  was  sent  into  the  market  under 
the  name  ammonia  soda.  But  as  the  ammonia  process  was 
given  up  after  a  time  because  it  could  not  compete  with 
the  Leblanc  process,  there  must  have  been  difficulties  in 
the  way  of  carrying  out  the  reactions  on  a  manufacturing 
scale.  These  difficulties,  which  are  chiefly  mechanical,  and 
are  due  to  the  stoppage  of  the  pipes  by  salts  that  separate 
during  the  process,  were  finally  overcome  by  Solvay.  Almost 
the  whole  of  the  world's  gigantic  demand  for  soda  is  now 
satisfied  by  the  use  of  the  Solvay  process. 


1 88  CHEMISTRY   IN    DAILY   LIFE 

The  process  is  carried  out  somewhat  as  follows.  Ammonia 
gas  is  pumped  into  a  solution  of  common  salt,  in  a  closed 
apparatus,  and  when  sufficient  ammonia  is  present  carbonic 
acid  gas  is  then  forced  into  the  solution.  Bicarbonate  of 
ammonium  is  thus  formed  in  the  liquid,  and  by  reacting 
with  the  sodium  chloride,  this  salt  produces  bicarbonate  of 
soda  which  separates  as  a  solid. 

The  common  salt  required  for  the  process  is  got  from  the 
salt  mines,  or  salt  brine  is  pumped  directly  from  the  salt- 
bearing  strata,  and  the  ammonia  that  is  needed  comes  from 
the  gas  works.  The  large  quantities  of  carbonic  acid  that  the 
process  demands  are  obtained  by  calcining  chalk  in  ovens, 
and  the  gas  that  is  given  off  is  forced  by  air-pumps  into  the 
brine. 

When  chalk  is  calcined  in  lime  kilns  it  separates  into  lime 
and  carbonic  acid  gas ;  as  carbonic  acid  is  also  produced 
by  the  burning  of  the  carbonaceous  fuel  used  for  heating  the 
kilns,  the  gases  given  off  from  these  kilns  are  very  rich 
in  carbonic  acid,  and  they  are  used  in  many  industries, 
besides  soda  making,  wherein  that  gas  is  required. 

The  bicarbonate  of  soda  obtained  in  the  way  described  has 
to  be  transformed  into  "  soda,"  which  is  the  normal  carbonate. 
To  do  this  it  is  only  necessary  to  calcine  the  bicarbonate  at  a 
moderate  temperature,  whereby  the  second  molecule  of 
carbonic  acid  is  driven  off. 

The  liquids  drawn  off  from  the  bicarbonate  of  soda 
contain  salammoniac ;  and  as  a  matter  of  course  ammonia 
is  recovered  from  these  liquids.  Ammonia  is  driven  out 
from  its  combinations  by  any  base  that  is  stronger  than 
itself;  when,  therefore,  these  solutions  are  boiled  with  caustic 
lime,  which  is  produced  in  the  lime  kilns  of  the  soda  factory 
along  with  carbonic  acid,  ammonia  is  driven  out  by  the  more 
basic  lime.  The  ammonia  obtained  in  this  way  is  pumped 


AMMONIA  SODA   PROCESS  189 

into  a  fresh  lot  of  brine,  and  the  manufacture  goes  on  unin- 
terruptedly. 

The  final  bye-product  of  the  manufacture  is  the  chloride  of 
calcium  produced  by  boiling  the  solutions  of  salammoniac 
with  lime. 

Chloride  of  ammonium  -f  lime  =  chloride  of  calcium  -f  ammonia. 

This  solution,  or  the  solid  chloride  of  calcium  produced  by 
evaporating  this  solution,  has  not  yet  found  any  special 
application,  and  there  is  nothing  to  be  done  with  the  large 
quantities  of  this  substance  that  accumulate  in  the  ammonia 
soda  works  except  to  run  them  into  the  nearest  river. 

It  is  evident  that  the  chlorine  which  is  originally  brought 
into  the  process  in  the  form  of  chloride  of  sodium  is  not  used 
in  the  Solvay  process,  but  is  thrown  away  as  chloride  of 
calcium.  In  the  Leblanc  process,  on  the  other  hand,  the 
chlorine  of  the  common  salt  is  recovered  as  hydrochloric  acid, 
which,  either  as  it  is  or  when  transformed  into  bleaching 
powder,  etc.,  has  a  considerable  value. 

Only  the  initial  stage  of  the  Leblanc  process  has  remained. 
There  are  factories  where  common  salt  is  heated  with  sulphuric 
acid,  to  obtain  hydrochloric  acid.  But  these  factories  do  not 
work  up  the  sulphate  of  soda  which  they  obtain  into  soda  ; 
they  sell  it  for  glass-making  (see  Lecture  X.).  Nor  do  they 
make  chlorine  from  their  hydrochloric  acid,  but  seek  to  sell  it 
to  other  industries  which  use  that  acid.  The  reason  for  this 
is  as  follows.  The  electric  current  (of  the  action  of  which  we 
shall  learn  something  in  Lecture  XI.)  is  able  to  decompose 
many  substances  into  the  elements  of  which  they  are  com- 
posed. Chlorine  can  be  obtained  by  decomposing  chloride  of 
sodium  (common  salt),  or  chloride  of  potassium — plentifully 
supplied  by  the  Stassfurt  deposits  (see  p.  46) — by  the  electric 
current  ;  and  electricity  is  now  to  be  had  at  a  cheap  rate. 


1 90  CHEMISTRY  IN   DAILY  LIFE 

The  other  products  of  the  action  of  the  current  on  these  salts 
are  caustic  soda  and  caustic  potash  respectively.  We  shall 
find  that  these  alkalis  are  used  in  making  soaps  ;  of  their  use 
in  paper  making  we  know  already. 

These  things  do  not  seem  to  be  in  keeping  with  the  dicta 
of  moral  philosophy  which  tell  us  that  every  worthy  piece  of 
work  receives  its  reward.  We  see  here  that  a  good  piece  of 
work  demolishes  another  equally  good,  and  that  progress  is 
made  by  the  new  constantly  replacing  the  old. 

Although  the  consumption  of  soda  is  very  great,  and  soda 
has  driven  potash  out  of  many  industries,  nevertheless  there  is 
still  a  very  considerable  demand  for  potash.  The  chief  source 
of  potash  salts  is  wood  ashes,  which  in  recent  years  comes  in 
large  quantities  from  the  Caucasus.  Two  quite  new  sources 
of  potash  salts  have,  however,  been  made  available  since  the 
middle  of  last  century  ;  these  are  molasses  and  the  washings 
of  wool. 

Molasses  is  the  name  given  to  the  final  mother-liquor  in  the 
manufacture  of  sugar  (see  p.  76).  Although  means  are  now 
known  for  extracting  the  sugar  from  molasses,  yet  a  great 
deal  of  this  substance  is  still  used  for  making  spirits  by 
fermentation.  The  residue  that  is  left  (see  p.  107)  when  the 
spirit  is  distilled  off  from  beetroot  molasses  has  no  value  as  a 
food,  as  it  contains  only  the  salts  that  were  originally  present 
in  the  beets  and  went  into  solution  when  the  beets  were 
macerated  with  water.  These  salts,  coming  as  they  do 
from  the  soil,  are  rich  in  potash  ;  if  the  molasses  residue  is 
evaporated  to  dryness  and  calcined  the  potash  salts  can  be 
obtained  by  then  lixiviating  with  water. 

The  second  source  of  potash  salts  mentioned  above  is  more 
remarkable.  Factories  have  been  established  for  washing  the 
crude  wool  that  is  brought  in  large  quantities  into  Europe, 


SOAP  MAKING  igi 

chiefly  from  Australia,  Africa,  and  South  America.  The 
grease  that  is  taken  out  of  the  wool  by  the  washing  accumu- 
lates in  the  wash  water,  and  this  grease  has  been  found  by 
experiment  to  be  rich  in  potash  salts  ;  these  salts  are  obtained 
by  evaporating  the  wash  water  to  dryness,  calcining,  and 
extracting  with  water.  Considerable  quantities  of  potash 
salts  are  obtained  from  this  source,  and  the  extraction  of 
these  salts  has  become  a  paying  process. 

Neither  carbonate  of  potash  nor  carbonate  of  soda  is 
directly  applicable  to  the  making  of  soap,  which  is  the  subject 
we  have  now  to  consider.  These  compounds  do  not  act  upon 
the  fats  from  which  soap  is  manufactured.  The  carbonates  of 
potash  and  soda  must  be  transformed  into  caustic  potash  and 
caustic  soda  respectively.  This  is  done  in  the  following  way, 
if  the  caustic  alkali  is  not  obtained  directly  by  an  electrolytic 
process,  a  method  which  has  become  possible  in  the  last  few 
years. 

We  know  (p.  176)  that  limestone  is  decomposed,  by  heating, 
into  carbonic  acid  and  caustic  lime.  One  might  expect  that 
carbonate  of  potash  and  carbonate  of  soda  would  be  changed 
by  heat  into  carbonic  acid  and  caustic  alkali  ;  but  experiment 
shows  that  this  is  not  practicable.  These  two  compounds  do 
not  decompose  even  at  very  high  temperatures.  Unlike 
limestone,  the  carbonates  of  potash  and  soda  dissolve  in  water. 
If  burnt  lime  is  added  to  these  solutions,  the  lime  withdraws 
and  combines  with  the  carbonic  acid,  forming  carbonate  of 
lime,  and  caustic  potash  or  caustic  soda.  As  carbonate  of 
lime  is  insoluble  in  water,  it  sinks,  and  the  supernatant  liquid 
can  be  drawn  off.  The  following  equations  show  what  occurs  : 

Carbonate  of  potash   -f  caustic  lime  =  caustic  potash  +  carbonate  of 

lime. 
Carbonate  of  soda  +  caustic  lime  =  caustic  soda  +  carbonate  of  lime. 


IQ2  CHEMISTRY  IN   DAILY  LIFE 

The  caustic  lye  of  the  soap  maker  can  thus  be  prepared. 
When  this  lye  is  boiled  with  fats,  which,  as  we  know,  are 
compounds  of  glycerin  with  fatty  acids  (see  p.  19),  the 
decomposition  represented  in  the  following  scheme  occurs : 

Compounds  of  glycerin  and  fatty  acids  +  alkali  =  compounds  of  alkali 
and  fatty  acids  +  glycerin. 

Soap  is  a  mixture  of  compounds  of  fatty  acids  with  alkali. 

We  are  told  by  the  elder  Pliny  that  the  Germans  prepared 
an  ointment  by  boiling  ashes  with  fat ;  but  it  was  not  until 
about  the  second  century  A.D.  that  this  substance  began  to  be 
used  for  cleansing  purposes,  although  at  that  time  and  for 
some  time  afterwards  it  continued  to  be  employed  more  as  a 
medicament  than  a  detergent.  We  know  that  Marseilles 
boasted  a  flourishing  soap  industry  about  the  year  1000,  and 
that  it  was  not  till  the  fifteenth  century  that  the  Venetian 
factories  entered  into  competition  with  Marseilles ;  from 
that  time  the  art  of  soap  making  spread  gradually  over  the 
world. 

The  manufacture  of  soap  remained  a  purely  empirical 
handicraft,  as  nothing  was  known  of  the  chemical  changes 
involved  in  the  processes,  until,  in  the  early  years  of  the 
nineteenth  century,  the  French  chemist  Chevreul  made 
known  the  nature  of  the  fats,  showing  them  to  be  compounds 
of  glycerin  with  fatty  acids.  This  discovery  threw  light 
on  the  processes  of  soap  making  ;  and  when,  in  addition 
to  this,  the  soap  maker  was  able  to  use  the  comparatively 
cheap  caustic  soda  as  well  as  the  more  expensive  potash,  the 
manufacture  of  soap  began  to  expand,  and  this  went  on  until 
to-day  soap  has  been  brought  within  the  reach  of  even  the 
poorest  person. 

The  fact  that  the  only  fats  at  the  disposal  of  the  soap 
maker  were  animal  tallow  and  olive  oil  gave  a  certain  stability 


HARD  AND  SOFT  SOAPS  193 

to  the  soap  industry  in  older  times  ;  but  the  extension  of 
commerce  is  now  constantly  bringing  new  kinds  of  fat 
and  new  oils  into  the  soap  factories,  and  these  require  special 
methods  of  treatment,  and  demand  much  consideration  on 
the  part  of  the  manufacturer  if  he  is  to  retain  his  position 
in  competition  with  his  ever-active  neighbours. 

Every  one  knows  the  statement,  All  misfortunes  come  from 
change.  This  saying  comes  to  our  minds  in  the  present 
instance.  But  it  would  be  better  to  say,  Every  advance  comes 
from  change.  For  we  certainly  do  not  share  the  opinion  that 
it  would  be  a  fortunate  thing  for  us  to  stand  still  in  the 
old  ways  of  the  centuries  that  are  past. 

Fat  is  nowadays  a  bye-product  of  many  industries  ;  this  is 
true,  for  instance,  of  the  fat  from  bones.  We  have  already 
spoken  in  some  detail  of  the  ways  in  which  bones  are  most 
advantageously  made  use  of  (see  p.  44).  The  fat  of  bones  is 
of  no  value  for  the  purposes  we  have  spoken  of,  and  it  is 
therefore  removed  before  the  bones  are  used.  It  used  to  be 
the  custom  to  boil  the  bones  vigorously  with  water  ;  the  fat 
was  then  separated  and  rose  to  the  surface  of  the  water.  But 
this  method  did  not  completely  remove  the  fat. 

The  method  now  in  use  consists  in  breaking  up  the  bones 
into  suitable  pieces,  and  then  extracting  with  petroleum  ether 
in  special  apparatus  ;  the  whole  of  the  fat  is  obtained  in 
solution  by  this  process. 

The  chief  difference  between  soaps  made  by  the  use 
of  potash  and  those  made  by  using  soda  is  that  the  former 
are  soft  soaps  while  the  latter  are  hard  soaps. 

The  process  for  making  soft  soap  consists  in  boiling  the 

cheapest  kinds  of  soluble   oils,   such  as   fish  oil,  hemp  oil, 

or  linseed  oil  (and,  since   1910,  oil  made  from  the  seeds  of 

the  soy  plant),  with  potash  lye  in  iron  vessels.     If  the  lye  is 

13 


194  CHEMISTRY   IN   DAILY  LIFE 

allowed  to  act  slowly  the  soap  may  be  taken  to  be  ready 
when  the  contents  of  the  vessels  have  acquired  a  pasty 
consistency.  Soap  made  in  this  way  does  not  dry  in  the  air, 
but  always  remains  soft.  It  can  bear  a  good  deal  of  loading 
— that  is,  substances  may  be  added  to  it  pretty  freely  without 
their  presence  being  shown.  For  instance,  it  can  take  up 
a  considerable  quantity  of  water  glass  (that  is,  silicate  of  soda, 
to  be  spoken  of  later  under  glass)  ;  and  solutions  of  sulphate 
of  potash  and  other  substances  are  also  employed.  Such 
additions  are  useless  so  far  as  the  detergent  power  of  the  soap 
is  concerned,  but  they  serve  to  increase  the  weight  of  the 
soap,  and  as  these  loading  substances  are  cheaper  than  soft  soap 
it  is  possible  to  sell  loaded  soap  at  an  extremely  low  price. 

Until  a  method  for  making  soda  was  worked  out,  in  the 
way  already  described,  the  only  alkali  available  for  making 
soap  was  caustic  potash  got  from  potashes,  and  therefore 
soft  soap  was  the  only  soap  that  could  be  manufactured 
directly.  But  the  discovery  was  made  at  an  early  stage  of 
the  manufacture  that  the  addition  of  common  salt  after 
boiling  the  fat  with  caustic  potash  produced  a  marked  change 
in  the  product.  The  effect  of  salting  is  to  cause  the  separation 
of  a  liquid  which  lies  beneath  the  soap  and  can  be  drained  off, 
and  also  to  make  the  soap  carry  with  it  much  less  water  and 
to  cause  it  to  separate  as  a  white  semi-solid  mass  which 
becomes  hard  when  it  is  cold. 

The  cause  of  this  change  is  found  in  the  reaction  which 
takes  place  between  the  common  salt  (chloride  of  sodium) 
and  the  potash  salts  of  the  fatty  acids,  resulting  in  the  pro- 
duction of  chloride  of  potassium  and  soda  salts  of  the  fatty 
acids. 

Potash  salts  of  fatty  acids  -f  Chloride  of  sodium  =  Soda  salts  of  fatty  acids  + 

Soft  soap.  Common  salt.  Hard  soap. 

Chloride  of  potassium. 


TOILET  SOAPS— FITTED  SOAPS  195 

The  fatty  salts  of  soda  are  not  able  to  combine  with 
all  the  water  which  comes  from  the  lye ;  some  of  this  water 
therefore  separates  as  a  liquid  underlayer,  and  this  layer  also 
contains  in  itself  the  glycerin  that  has  been  separated  from 
the  fats  by  the  process  of  saponification,  and  the  chloride  of 
potassium  ;  these  two  are  thus  removed  in  the  watery  layer. 
If  one  salting  is  not  sufficient  the  process  is  repeated.  The 
genuine  toilet  soaps  are  formed  by  the  solidification  of  the 
fatty  salts  separated  by  this  process.  As  the  salting  is  never 
completely  effective,  these  toilet  soaps  always  contain  some 
of  the  fatty  salts  of  potash,  that  is  some  non-solidifying  soap, 
and  it  is  this  which  gives  them  their  pleasant  softness.  One 
hundred  parts  of  tallow  treated  in  the  way  described  yield 
about  160  parts  of  good  soap  containing  from  10  to  20  per 
cent,  of  water. 

But  the  greater  part  of  the  soda  soaps  made  at  present  are 
made  by  boiling  fats  with  caustic  soda — that  is  to  say,  by 
a  process  which  yields  hard  soaps  directly. 

Hard  soaps  can  be  loaded  as  well  as  soft  soaps.  If  the 
product  of  saponification  is  boiled  with  water  for  a  long  time, 
and  is  then  let  cool,  the  soap  solidifies  to  a  hard  mass  without 
the  separation  of  a  watery  under-layer.  Such  soap  contains 
about  50  per  cent,  of  water  ;  it  is  known  as  fitted  soap. 

High-class  loaded  soda  soaps  are  best  prepared  with  the 
help  of  cocoanut  oil.  The  white  pulp  of  the  fruit  of  the 
cocoa  palm,  which  grows  in  tropical  countries,  is  dried  and 
exported  to  Europe,  where  a  fat  is  extracted  amounting  to 
about  68  per  cent,  of  the  weight  of  the  substance.  This  fat 
melts  at  about  21°  C.  [about  70°  F.] ;  it  is  therefore  fairly 
solid  at  ordinary  temperatures,  and  because  of  its  consistency 
is  known  as  cocoanut  butter. 

Attempts  have  been  made  to  prepare  a  substitute  for 
butter  from  this  substance  by  removing  the  more  volatile 


196  CHEMISTRY   IN   DAILY   LIFE 

ingredients  by  passing  superheated  steam  into  the  liquefied 
oil,  stirring  the  oil  at  the  same  time  with  soda  solution 
whereby  the  free  fatty  acids  are  neutralised,  drawing  off  the 
melted  oil  and  letting  it  solidify.  A  butter-like  substance 
quite  free  from  rancid  taste  is  thus  obtained  which  is  harm- 
less, and  serves  as  the  starting  point  for  making  a  substitute 
for  butter  (see  p.  65). 

Soap  is  not  made  from  cocoanut  oil  alone,  because  of  the 
very  disagreeable  odour  which  always  persists  in  this  oil, 
but  from  a  mixture  of  one  part  of  this  oil  and  two  parts 
of  palm  oil  and  a  little  tallow. 

The  palm  oil  is  derived  from  the  oil-yielding  palms  that  flour- 
ish on  the  west  coast  of  Africa  and  in  Central  America.  The 
flesh  of  the  fruit  and  the  seeds  of  these  palms  are  rich  in  oil. 
The  fruit  is  boiled  by  the  natives  to  obtain  the  oil,  and  the 
seeds,  which  are  very  hard,  are  sent  to  Europe,  where  they 
are  pressed.  These  seeds  yield  about  40  per  cent,  of  their 
weight  of  palm  fat,  and  the  residue  serves  as  an  excellent 
oil-cake  fodder,  especially  for  milk  cows  (see  p.  60). 

Cocoanut  oil  is  very  easily  saponified,  and  this  readiness 
to  undergo  saponification  belongs  also  to  mixtures  which 
contain  this  oil.  Complete  saponification  is  accomplished  by 
heating  to  about  40°  C.  [about  105°  F.],  which  is  much  under 
the  boiling-point,  with  concentrated  caustic  soda  lye  containing 
a  little  carbonate  of  soda ;  the  whole  liquid  solidifies  on 
cooling,  and  the  soap  is  made.  Inasmuch  as  all  the  water  of 
the  lye  is  enclosed  in  the  soap,  as  much  as  from  300  to  600 
parts  of  soap  are  obtained  from  100  parts  of  the  mixture  of 
oils — that  is  to  say,  nearly  twice  the  yield  that  is  got  from  tallow. 

Resin  soaps  are  often  spoken  of  nowadays.  A  good  soap, 
serviceable  for  ordinary  requirements,  cannot  be  made  from 
resins  alone — colophony  is  the  resin  chiefly  used — but  we  have 
already  seen  that  soap  solutions  made  by  boiling  resins  with 


ACTION   OF  LIME  ON    SOAPS  1 97 

soda  lye  are  used  for  sizing  paper  (see  p.  166).  But  if  soap 
is  being  made  from  tallow  or  palm  oil,  and  a  quantity  of  resin 
equal  to  about  half  the  amount  of  the  fat  that  would  normally 
be  employed  is  added,  in  place  of  fat,  to  the  boiling  soap 
paste,  this  resin  is  saponified  along  with  the  fat,  and  a  very 
cheap  and  very  useful  resin-fat  soap  is  obtained. 

Genuine  soaps  then  are  prepared  by  boiling  tallow  or  other 
similar  fat,  or  oils,  with  caustic  soda  or  caustic  potash  lye. 
Now  we  know  that  there  are  many  other  alkalis  besides  soda 
and  potash,  hence  there  must  be  other  compounds  of  fatty 
acids  and  alkalis  besides  those  that  are  known  as  hard  soap 
and  soft  soap. 

The  strongest  alkali,  in  the  chemical  meaning  of  the  term, 
is  burnt  lime.  Now  the  compound  of  lime  with  the  fatty 
acids  that  is  indicated  by  theory  has  been  actually  prepared. 
But  this  compound  is  insoluble  in  water  ;  when  it  is  mixed 
with  water  it  sinks  to  the  bottom  as  any  other  insoluble 
powder  would  do,  and  the  water  does  not  froth  when  shaken 
up,  nor  has  it  any  of  the  other  properties  that  belong  to  a 
solution  of  soap.  This  substance  is  indeed  exceedingly 
inconvenient  in  everyday  life.  Because  of  its  insolubility  in 
water  it  precipitates  whenever  an  opportunity  is  given  for  its 
formation  ;  if  we  bring  soda  soap  or  potash  soap  into  ordinary 
water  this  compound  of  lime  with  the  fatty  acids  of  the  soap 
is  produced.  It  is  well  known  that  all  kinds  of  waters,  except 
distilled  water,  contain  more  or  less  chalk  ;  hence  whenever 
soap  is  brought  into  ordinary  water  used  for  domestic 
purposes  this  lime  compound  is  formed,  and  so  much  of  the 
fatty  acids  of  the  soap  as  enters  into  combination  with  lime 
ceases  to  be  available  for  washing  purposes.  The  more  chalk 
a  water  contains  the  more  of  this  lime  compound  is  formed, 
and  therefore  the  greater  is  the  destruction  of  soap.  For  it  is 
only  after  all  the  lime  has  been  combined  with  the  fatty  acids 


198  CHEMISTRY  IN  DAILY  LIFE 

of  the  soap  that  the  water  can  have  the  properties  of  a  solution 
of  soap  and  can  exert  those  detergent  effects  for  which  we 
use  soap  and  water. 

It  is  customary,  then,  in  daily  life,  to  distinguish  between 
soft  wafers  and  hard  waters.  The  soft  waters,  such  as  river 
water,  are  poor  in  chalk,  and  only  a  little  soap  is  needed  to 
make  these  waters  lather ;  but  hard  waters,  such  as  spring 
water,  contain  much  chalk,  and  they  consume  a  considerable 
quantity  of  soap,  reacting  with  it  to  form  lime  salts  of  the 
fatty  acids  of  the  soap,  before  a  lather  begins  to  be  produced. 

The  compounds  of  lime  with  the  fatty  acids  that  are 
contained  in  soaps  cannot  be  used  for  washing  purposes ;  but 
the  state  of  affairs  is  different  when  oxide  of  lead  is  used 
as  an  alkali  and  fats  are  boiled  with  this  substance.  A 
compound  of  lead  with  the  fatty  acid  is  formed — that  is  to 
say,  a  lead  soap  is  produced  ;  and  this  compound  is  of  the 
nature  of  a  plaster.  Plasters  are  substances  more  tenacious 
and  harder  than  ointments,  and  they  are  used,  just  as  oint- 
ments are  used,  as  healing  agents  for  external  application. 
Pure  lead  soaps  are  used  as  plasters,  and  also  lead  soaps 
modified  by  additions  of  very  different  sorts  of  materials. 
The  German  sticking  plaster,  for  instance,  is  a  mixture, 
spread  on  linen,  of  500  parts  lead  soap,  to  which,  heated  to 
60°  or  80°  C.  [about  140°  to  175°  R],  50  parts  of  wax  are 
added,  and  also  50  parts  of  a  mixture  of  melted  dammar 
resin  and  colophony,  and  5  parts  of  turpentine.  The  English 
sticking  plaster  is  an  altogether  different  preparation.  It  is 
made  by  stretching  strips  of  woven  silk  cloth  on  a  frame,  and 
brushing  over  these  a  solution  of  the  very  best  glue  in  dilute 
spirit  until  a  piece  adheres  firmly  to  the  hand,  after  being 
moistened.  The  preparation  is  slightly  perfumed  with  a  little 
gum  benzoin,  or  a  similar  substance. 


LECTURE   X 

Glass — Glass  mirrors — Potash  and  soda  glass — Quartz  glass — Strass — 
Artificial  precious  stones — Ruby  glass — Milk  glass — Clay — Bricks — 
Mortars — Lime  sandstone  bricks  —  Cements — Glazing — Pottery 
—  Stoneware  —  Majolica  ware  —  Porcelain  —  Photography — Lunar 
caustic — Chloride,  bromide,  and  iodide  of  silver — Daguerreotypes — 
Development  of  the  negative — Talbotypes — Albumen  methods — Wet 
collodion  processes — Dry  silver  bromide  emulsion  plates — Platino- 
types — Photography  of  the  spectrum — Red  light — Orthochromatic 
plates — Colour  photography — Chromegelatin — Pigment  printing — 
Rontgen  rays — Radio-activity — Radium. 

IN  speaking  of  the  manufacture  of  soap,  mention  was  made 
of  silicate  of  soda,  or  water  glass,  which  is  a  very  soluble  salt 
that  is  used  for  loading  soft  soaps.  This  salt  and  silicate  of 
potash  are  the  only  compounds  of  silicic  acid  that  are  soluble 
in  water.  But  these  salts  also  become  insoluble  in  water 
when  they  are  mixed  with  other  silicates  and  the  mixtures 
are  melted.  For  instance,  if  silicic  acid,  potash,  and  lime 
are  fused  together  the  product  contains  silicate  of  potash 
and  silicate  of  lime,  and  is  insoluble  in  water.  This  product 
is  called  glass  when  it  has  been  prepared  with  proper  skill 
and  has  been  brought  into  such  a  form  as  makes  it  useful 
to  us. 

In  making  glass  the  practice  has  long  been  to  melt  together 
silicic  acid,  potashes  (that  is,  carbonate  of  potash),  and 
carbonate  of  lime  ;  the  carbonic  acid,  which  is  driven  out 

from  the  melted  compounds  by  the  silicic  acid,  escapes  as  gas, 

199 


200  CHEMISTRY   IN   DAILY  LIFE 

and  there  remains  a  mixture  of  silicate  of  potash  and  silicate 
of  lime. 

Silicic  acid  +  carbonate  of  potash  =  silicate  of  potash  +  carbonic  acid. 
Silicic  acid  +  carbonate  of  lime  =  silicate  of  lime  +  carbonic  acid. 

The  salts  of  silicic  acid  are  called  silicates  in  chemical 
nomenclature  ;  and  glass  may  be  described  as  a  mixture 
of  several  silicates  [or  salts  allied  to  silicates]  melted  together. 
This  description  may  be  applied  in  a  very  general  way ;  it 
is  not  necessary  to  keep  to  silicic  acid,  potash,  and  carbonate 
of  lime  ;  as  a  matter  of  fact,  in  glass  making  sometimes  one 
and  sometimes  another  of  these  constituents  is  replaced 
wholly  or  in  part  by  another  acid  or  by  other  bases  which 
experience  has  proved  to  be  suitable  for  the  objects  of  the 
manufacture.  We  shall  have  to  speak  of  the  most  important 
of  these  materials. 

A  very  high  temperature  is  required  for  melting  the 
materials  that  have  been  mentioned.  This  fact  is  sufficient 
of  itself  to  relegate  Pliny's  story  of  the  discovery  of  glass  to 
the  domain  of  fable.  According  to  that  story  certain 
Phoenician  merchants  had  made  a  fire  under  a  vessel  which 
they  had  supported  on  lumps  of  "  soda  "  ;  *  the  soda  melted 
by  the  heat,  and  coming  into  contact  with  sand  (that  is,  with 
silicic  acid),  and  the  other  necessary  materials  on  the  ground, 
produced  glass.  Now  such  a  fire  as  that  described  in  Pliny's 
story  could  not  have  been  hot  enough  to  melt  glass.  At  the 
same  time  we  need  not  be  astonished  at  finding  glass  objects 
in  very  ancient  tombs,  since  we  know  that  the  art  of 
smelting  metals  was  practised  from  very  early  times  and 
this  art  requires  the  maintenance  of  high  temperatures. 

*  The  term  used  by  Pliny  is  generally  translated  soda  \  but  it  is 
certain  that  Pliny  was  not  acquainted  with  the  substance  that  we  now 
call  by  this  name. 


GLASS  201 

Glass  was  exceedingly  costly  in  the  old  classical  days. 
The  most  famous  glass  factory  of  the  Middle  Ages  was  at 
Murano  near  Venice,  and  this  factory,  after  nearly  collapsing, 
has  been  revived  in  our  own  times.  Glass  is  manufactured 
to-day  in  every  country  where  the  cost  of  labour  is  not 
too  great. 

The  employment  of  glass  in  windows,  for  which  purpose 
nothing  can  replace  it,  came  in  very  gradually  because  of 
the  high  price  of  the  material.  Although  the  windows  of 
churches  had  been  filled  with  glass  as  early  as  the  tenth 
century,  yet  it  was  not  until  about  the  fourteenth  century 
that  glass  began  to  be  used  in  the  windows  of  the  private 
houses  of  the  rich,  and  several  centuries  passed  before  it  had 
completely  taken  the  place  of  the  oiled  paper,  the  stretched 
animal  bladders,  and  the  solid  window  shutters  of  that  period. 
The  extraordinary  gladness  wherewith  the  German  singers 
of  the  early  Middle  Ages  greeted  the  return  of  spring  may 
have  had  some  connection  with  these  window  coverings. 
Men  escaped  in  spring  from  the  wretchedness  of  spending 
the  long  days  of  winter  in  half-darkened  rooms  lighted  by 
the  feeble  glimmer  of  burning  pine-splinters. 

Glass  making  then  requires  silicic  acid.  This  is  ready  to 
hand  either  in  the  form  of  sand,  which  is  silicic  acid,  or  in 
the  form  of  quartz,  which  is  crystallised  silicic  acid.  The 
purer  the  raw  material  the  better  is  the  result.  The  presence 
of  iron  is  prejudicial,  for  the  silicate  of  iron  which  would  be 
formed  in  the  manufacture  is  very  dark-coloured  ;  and  it  is 
the  presence  of  this  salt  in  cheap  glass  that  gives  that  glass 
its  dark  colour.  This  colour  is  also  sometimes  given  to 
wine  glasses.  In  older  times  all  window  glass  was  greenish, 
because  sand  is  seldom  found  quite  free  from  iron  ;  but  the 
modern  means  of  transport  enable  pure  sand  to  be  sent 
anywhere. 


2O2  CHEMISTRY   IN   DAILY   LIFE 

In  a  very  few  cases  silicic  acid  is  partially  replaced  by  the 
much  more  expensive  boric  acid.  This  acid  produces  a  very 
lustrous  glass  which  is  especially  useful  in  making  certain 
optical  instruments. 

As  every  variety  of  glass  must  contain  either  potash  or 
soda,  only  potash  glass  was  manufactured  in  older  times 
because  only  potash,  in  the  form  of  potashes,  was  available. 
The  use  of  potashes  was  also  connected  with  the  fact  that, 
in  Germany  at  any  rate,  glass  factories  were  generally  located 
in  forests,  for  not  only  did  the  forests  provide  fuel  for  heating 
the  furnaces,  but  the  ashes  of  the  burnt  wood  provided 
potashes,  and  if  more  potashes  were  required  it  could  easily 
be  obtained  on  the  spot. 

After  a  time  soda  began  to  be  used  as  a  substitute  for 
potash ;  but  when  the  manufacture  of  soda  was  established, 
a  cheaper  substitute  for  potash  than  soda  was  forthcoming. 
We  know  that  the  first  stage  in  making  soda  by  Leblanc's 
process  was  the  conversion  of  common  salt  into  sulphate  of 
soda.  Now  sulphate  of  soda  may  be  used  in  glass  making 
in  place  of  soda  ;  it  is  only  necessary  to  mix  the  sulphate  of 
soda  with  coal,  or  charcoal,  in  order  that  silicate  of  soda  may 
be  formed  in  the  reaction  with  silicic  acid.* 

Carbonate  of  lime  is  generally  used  in  the  form  of  chalk 
because  chalk  is  easily  obtained  free  from  obnoxious  in- 
gredients, especially  free,  or  nearly  free,  from  iron  ;  some 

*  The  reaction  proceeds  in  this  way  :  while  the  silicic  acid  combines 
with  the  soda  the  coal  reacts  with  the  sulphuric  acid,  which  is  the  other 
constituent  of  sulphate  of  soda,  and  at  the  high  temperature  of  the 
furnace  the  coal  robs  the  sulphuric  acid  of  part  of  its  oxygen,  forming 
monoxide  of  carbon,  which  escapes  as  a  gas,  and  leaving  sulphurous 
acid,  which  being  also  a  gas  passes  off  (see  the  reverse  process  described 
on  p.  1 80).  Hence  none  of  the  sulphur  that  was  originally  present  in 
the  sulphate  of  soda  employed  remains  in  the  finished  glass. 


GLASS-MAKING  203 

specimens  of  chalk  are  indeed  perfectly  pure  carbonate  of 
lime.  A  whole  series  of  other  bases  may  be  used  in  making 
glass  in  place  of  lime ;  lead  oxide  is  one  of  those  that  is 
often  employed  (for  more  detaUs  see  p.  206). 

Finally,  the  glass  works  melt  up  old  glass  with  the 
materials  for  making  new,  and  for  this  reason  most  of  the 
broken  glass  finds  its  way  back  to  the  furnaces. 

When  the  materials  for  making  glass  have  been  thoroughly 
mixed  by  machinery  they  are  melted  together  in  large  pots. 
It  is  of  course  desired  to  get  a  high  temperature  in  the 
melting  ovens  with  the  minimum  consumption  of  fuel,  and  for 
this  reason  these  ovens  are  generally  worked  nowadays  with 
regenerative  gas  furnaces.  We  shall  consider  the  arrangement 
of  these  furnaces  when  we  are  dealing  with  the  iron  industry. 

The  glass  blower  removes  some  of  the  molten  glass  from 
the  furnace  on  the  end  of  his  rod,  and  by  blowing  into  the 
other  end  of  this  rod  he  is  able  to  cause  the  glass  to  assume 
almost  any  shape  he  pleases  ;  if  the  object  to  be  made  is 
very  complicated  the  aid  of  a  second  workman  is  needed. 
The  glass  blower's  rod  is  nothing  but  a  piece  of  metal  tube 
covered  with  wood  in  the  middle,  so  that  it  may  be  handled 
when  hot.  Since  1908,  the  making  of  ordinary  bottles  has 
been  conducted  by  using  machines  invented  by  an  American 
named  Owen.  About  £50,000  was  spent  in  perfecting  the 
invention.  The  European  glass  makers  have  spent  about 
£750,000  in  acquiring  the  patent  rights.  By  this  method, 
two  workmen,  with  three  boy-helpers,  can  turn  out  20,000 
bottles  daily  ;  to  do  this  used  to  require  eighty  glass-makers. 
When  the  glass  has  been  shaped  to  the  desired  form  it  is 
brought,  while  still  hot,  into  the  annealing  oven,  where  the 
process  of  cooling  goes  on  very  slowly  over  a  period  of  a  few 
days  ;  if  this  were  not  done  the  glass  would  be  so  brittle  as 


204  CHEMISTRY   IN   DAILY  LIFE 

to  be  practically  useless.  It  should  be  remarked  that  glass 
for  windows  is  made  in  the  way  described.  The  workman 
blows  as  large  an  oblong  cylinder  as  possible  ;  this  is  cut  off 
by  shears,  and,  being  still  very  soft,  is  flattened  out,  and  then 
put  into  the  annealing  oven,  from  which  it  comes  as  a 
finished  pane. 

The  discovery,  made  in  the  seventeenth  century,  that  glass 
can  be  cast  was  of  great  importance.  For  this  purpose 
molten  glass  is  poured  on  a  metal  table,  of  sufficient  size, 
furnished  with  a  raised  edge.  All  those  large  panes  of 
plate  glass  that  we  see  in  shops  nowadays  are  made  by 
cutting  sheets  of  cast  glass.  As  these  sheets  can  be  cast  of 
considerable  thickness  they  may  be  made  strong  enough  to 
be  used  for  letting  into  floorings  to  give  light  to  rooms 
beneath.  When  used  for  this  purpose  the  glass  is  of  course 
not  ground. 

Plate  glass  is  also  used  for  making  the  glass  mirrors  that 
have  completely  driven  out  the  metal  mirrors  of  former  times. 
Before  glass  mirrors  were  invented  finely  polished  plates  of 
silver,  or  of  a  very  white  alloy  made  of  two  parts  of  copper 
and  one  part  of  tin,  were  used  as  mirrors.  But  these  metallic 
mirrors  were  very  inconvenient  because  of  the  sensitiveness 
of  the  surfaces,  especially  the  surface  of  silver,  which  is  so 
easily  blackened.  As  the  reflecting  surfaces  of  glass  mirrors 
are  protected  by  glass  these  mirrors  are  entirely  unaffected 
by  outside  influences. 

In  order  to  make  a  plate  glass  into  a  mirror  a  sheet  of 
tinfoil — that  is,  tin  beaten  very  thin — over  which  'mercury 
has  been  poured  is  laid  on  one  surface  of  the  glass.  The 
mercury  dissolves  the  tin,  forming  with  it  what  is  called  an 
amalgam  ;  and  this  amalgam  has  two  properties — it  reflects 
light  admirably,  and  it  adheres  very  firmly  to  glass.  The 


MIRRORS  2O5 

excess  of  mercury  is  drained  away  by  gradually  raising  the 
plate  from  its  original  horizontal  position  into  a  sloping 
position  ;  after  about  four  weeks  the  mirror  is  ready  for 
use. 

Mirrors  made  in  this  way  leave  hardly  anything  to  be 
desired.  But  the  process  is  extremely  risky  to  the  workmen, 
as  they  are  constantly  exposed  to  the  danger  of  mercury- 
poisoning  by  the  fumes  of  this  metal ;  for  mercury  volatilises 
slightly  even  at  the  temperature  of  an  ordinary  room. 

Chemists  have  long  been  acquainted  with  another  method 
for  making  mirrors  besides  that  wherein  tin  amalgam  is  used 
as  the  reflecting  surface  ;  in  this  other  method,  silver  deposited 
on  the  glass  forms  the  reflecting  surface  that  is  required. 
The  suggestion  to  use  this  method  on  the  large  scale  came 
from  England. 

The  foundation  of  the  process — the  exact  chemical  reactions 
cannot  be  made  clear  in  this  place — is  the  fact  that  it  is 
possible  to  prepare  solutions  of  silver  from  which  the  silver 
can  easily  be  precipitated  as  metal  by  the  addition  of  certain 
reagents.  If  the  conditions  are  properly  arranged  the  silver 
is  not  thrown  down  rapidly  as  a  powder,  but  is  precipitated 
very  gradually  in  the  form  of  an  extremely  lustrous,  mirror- 
like  coating  on  the  sides  of  the  vessel.  In  applying  this 
process  to  silvering  a  plate  of  glass,  the  properly  chosen 
mixture  is  poured  on  to  the  side  to  be  silvered,  and  after 
a  time  the  mirror  of  silver  is  formed.  As  silver  is  the  whitest 
of  all  the  metals  these  mirrors  are  superior  to  all  others,  and 
a  mirror  made  by  using  mercury  seems  dark  when  placed 
beside  one  made  by  the  silvering  method.  The  description 
of  the  preparation  of  these  mirrors  shows  that  the  manufacture 
is  quite  harmless  to  the  workpeople.  Nor  is  the  method 
expensive,  although  silver  is  the  metal  used.  Only  about  2j 
grams  of  the  metal  are  deposited  on  a  square  metre  of  surface 


2O6"  CHEMISTRY  IN   DAILY  LIFE 

[about   38  grains  on  lof  square  feet],  and  this  quantity  of 
silver  costs  to-day  only  about  twopence. 

The  statement  always  holds  good  that  potash  glass  is 
much  harder  to  melt  than  soda  glass.  For  this  reason 
apparatus  is  made  of  potash  glass  especially  for  the  use  of 
chemists  and  physicists.  Very  great  advances  have  been 
made  recently  in  preparing  the  glass  vessels  in  which  so 
many  substances  are  boiled  in  chemical  laboratories  ;  these 
advances  are  based  on  turning  to  the  best  account  our 
knowledge  of  the  chemical  and  physical  properties  of  glass. 
The  vessels  must  be  very  thin  in  order  that  they  may  be 
quickly  heated  equally  in  every  part ;  nevertheless  the 
frangibility  of  them  is  not  great  when  they  are  handled  by 
people  who  have  got  accustomed  to  working  with  them. 
Until  the  year  1895  ^  was  necessary  to  heat  glass  dishes  very 
carefully ;  but  glass  apparatus  is  now  to  be  had  in  which 
liquids  may  be  heated  to  about  180°  to  200°  C.  [about  350°  to 
390°  R],  and  which  may  then  be  plunged  into  cold  water 
without  breaking.  Such  an  improvement  as  this  was  hardly 
to  be  expected. 

Nevertheless  this  improvement  was  cast  into  the  shade  in 
the  year  1902.  In  that  year  it  was  found  possible  to  melt 
pure  quartz  in  the  electric  furnace  to  a  liquid  mobile  enough 
to  work  with  as  one  works  with  glass.  Vessels  made  of 
melted  quartz  are  not  glass  vessels  in  the  ordinary  meaning  of 
the  word.  Outwardly  they  cannot  be  distinguished  from 
ordinary  glass  vessels.  Because  of  the  difficulty  of  making 
them,  these  vessels  are  very  expensive.  They  are  quite 
indifferent  to  temperature  conditions.  They  may  be  heated 
to  redness  and  at  once  plunged  into  cold  water  without  suffer- 
ing the  slightest  hurt. 

The  most  easily  melted  glass  is  that  wherein  lead  oxide 


ARTIFICIAL  GEMS  207 

replaces  most  of  the  lime  of  ordinary  glass.  This  glass  is 
extremely  easily  manipulated,  and  those  prettily  ornamented 
plates,  dishes,  fyergnes,  and  the  like  that  are  much  used 
are  made  by  casting  this  kind  of  glass  in  moulds.  Moulded 
glass  does  not  of  course  show  the  sharp  edges  that  characterise 
cut  glass ;  but  the  price  of  the  former  is  very  much  less  than 
that  of  cut  glass  ware. 

The  name  strass  (or  paste)  is  given  to  the  glass  obtained 
by  melting  a  mixture  of  silicic  acid,  potashes,  and  lead  oxide 
without  the  addition  of  any  lime  ;  this  product  is  a  true 
double  silicate  of  potash  and  lead.  Strass  is  extremely 
lustrous  ;  indeed  it  sparkles  so  that  it  is  used  for  counterfeiting 
various  gems,  by  adding  to  it  appropriate  colouring  material. 
If  such  artificial  gems  are  skilfully  cut  and  polished  it  is 
impossible  to  distinguish  them  by  the  eye  alone  from  the 
genuine  stones.  But  as  lead  glass  is  soft  the  artificial  gems 
soon  get  scratched  by  handling,  and  in  this  respect  they  differ 
entirely  from  the  natural  precious  stones. 

The  colouring  of  glass  is  done  by  adding  suitable  sub- 
stances to  the  glass  when  it  is  molten  ;  the  addition  of  cobalt, 
for  instance,  produces  a  blue  colour.  The  most  beautifully 
coloured  glass  is  that  known  as  ruby  glass,  the  colouring 
matter  of  which  is  gold  added  in  the  form  of  a  suitable  com- 
pound called  gold  purple.  The  quantity  of  gold  used  is 
extremely  small.  This  glass  is  chiefly  used  for  making 
delicate  table  ornaments  and  things  of  that  character. 

The  artificial  gems  made  from  strass  are  almost  without 
value.  Naturally,  chemists  have  tried  to  make  genuine 
precious  stones  ;  they  have  succeeded,  as  we  know,  in  making 
alizarin  and  indigo.  The  first  successful  attempt  was  that 
of  Verneuil,  who  made  rubies  in  1902.  Analyses  have  shown 
that  rubies  consist  of  pure  alumina  coloured  by  a  trace  of 


208  CHEMISTRY  IN   DAILY   LIFE 

chromium  oxide.  Pure  alumina  is  extremely  hard  to  melt. 
It  acquires  the  special  properties  of  the  ruby  when  the  flame 
of  an  oxyhydrogen  blowpipe  [that  is,  a  blowpipe  which  burns 
hydrogen  in  an  atmosphere  of  oxygen]  is  made  to  play  on  a 
pellet  of  alumina,  placed  in  a  small  box,  on  to  which  a  very 
small  quantity  of  a  mixture  of  alumina  and  chromium  oxide 
falls  through  a  sieve.  A  little  rod  is  thus  formed  which 
gradually  increases  in  breadth  until  the  melted  mass  attains  a 
weight  of  50  carats  [200  grains].  Until  they  have  attained  to 
a  weight  of  about  5  carats,  artificial  rubies  are  not  to  be 
distinguished  from  natural  rubies  except  by  help  of  the 
microscope,  which  enables  them  to  be  differentiated  by  certain 
fine  fissures.  Natural  rubies  are  more  beautiful  the  larger 
they  are,  whereas  synthetic  rubies  lose  in  fineness  of  appear- 
ance as  they  become  larger ;  their  colour  seems  to  be  glaring 
and  coarse.  An  artificial  ruby  of  5  carats  might  cost  about 
ten  shillings  ;  a  natural  ruby  of  the  same  weight  was  valued 
at  £2$,  but  the  cost  has  decreased  of  late.  In  1909,  a  natural 
cut  ruby  of  extraordinarily  fine  colour,  weighing  39  carats, 
was  sold  in  London  for  ^"20,000. 

Artificial  sapphires  have  come  into  the  market  since  1910; 
these  stones  cannot  be  distinguished  by  any  tests  from  the 
natural  gems.  The  artificial  sapphires  cost  about  ten  shillings 

Der  carat,  whereas  the  natural  stone  has  hitherto  been  worth 

» 

about  £10  per  carat.  About  15,000  carats  of  artificial 
precious  stones  are  now  made  daily.  One  might  suppose  that 
purchasers  could  no  longer  be  found.  This  would  be  so  were 
the  stones  sold  only  as  ornaments.  But  because  of  their 
extraordinary  hardness,  these  artificial  gems  are  peculiarly 
adapted  for  use  in  the  watch-making  industry,  and  in  some 
branches  of  electrotechnics. 

Finally,  we  must  look  for  a  moment  at  milk  glass.     This  is 


CLAY— BRICKS  209 

obtained  by  adding  phosphate  of  lime,  generally  in  the  form 
of  bone  ash  (see  p.  42),  to  the  molten  glass.  A  clear  liquid 
is  obtained  ;  but  as  the  mass  cools  the  phosphate  of  lime 
separates,  and  the  desired  opacity  is  thus  given  to  the  glass. 
Some  other  substances  produce  the  same  effect  as  phosphate 
of  lime,  such  for  instance  as  cryolite^  which  is  a  mineral  from 
Greenland  containing  alumina  and  a  compound  of  sodium  and 
fluorine,  and  is  quite  free  from  iron.  The  milk  glass  made  by 
using  cryolite  is  especially  suitable  for  the  shades  of  lamps, 
because  the  flame  of  the  lamp  cannot  be  seen  through  this 
glass,  whereas  the  flame  appears  blood-red  through  glass 
manufactured  by  using  phosphate  of  lime. 


We  come  now  to  porcelain  and  pottery. 

There  are  certain  kinds  of  earth  found  in  many  places 
which  when  stirred  with  water  form  a  tenacious  mass  that  can 
be  moulded  and  kneaded.  Such  earths  are  called  clay,  and 
special  names  are  given  to  different  clays  in  accordance  with 
their  compositions  and  the  uses  to  which  they  are  put.  The 
commonest  kind  of  clay  generally  contains  a  good  deal  of 
sand  and  is  coloured  brownish  yellow  by  iron.  Bricks  are 
made  by  working  this  clay  into  oblong  pieces.  When  such 
bricks  have  been  dried  in  the  air  they  are  not  very  durable  ; 
indeed  a  shower  suffices  to  cause  them  to  run.  Still  they 
often  serve  to  fill  in  the  spaces  between  the  timbers  of  framed 
buildings. 

These  air-dried  clay  blocks  are  rendered  durable  and 
stone-like,  they  are  changed  into  true  bricks,  by  being  burnt. 
The  custom  used  to  be  to  build  up  alternate  layers  of  unburnt 
bricks  and  turf,  wood,  or  coal  into  heaps,  and  to  cover  these 
outside  with  clay,  so  that  when  the  combustible  material  was 


2IO  CHEMISTRY   IN   DAILY   LIFE 

ignited  the  bricks  got  very  strongly  heated.  But  this  method 
led  to  what  is  called  sintering — that  is  to  say,  the  easily 
fusible  parts  of  the  clay  became  nearly  liquid,  and  as  this 
semi-liquid  matter  cooled  it  bound  the  whole  heap  of  bricks 
into  one  mass.  Inasmuch  as  the  iron  compounds  in  the  clay 
are  changed  into  the  red  oxide  of  iron  during  the  burning  the 
burnt  bricks  are  red.  The  practice  to-day  is  to  burn  bricks 
in  what  is  called  a  ring  oven,  whereby  a  much  greater  effect 
is  obtained  from  the  materials  used  for  heating.  After 
a  thousand  years  without  competitors,  clay  bricks  have  found 
a  rival  in  bricks  made  from  calcareous  sandstone ;  we  shall 
speak  of  these  immediately. 

It  is  advisable  to  say  something  now  regarding  mortars^  as 
no  other  opportunity  will  occur  for  dealing  with  the  subject. 
The  mortar  that  is  generally  used  in  brick  buildings  is  a 
mixture  of  slaked  lime  and  sand.  We  know  that  when  lime- 
stone is  strongly  heated  it  separates  into  its  constituents, 
caustic  lime  and  carbonic  acid  (cf.  p.  177).  Caustic  lime  is  a 
solid  body  which  is  nearly  as  hard  as  unburnt  limestone ;  but 
it  possesses  the  remarkable  property  of  crumbling  to  powder 
when  it  is  brought  into  contact  with  water.  Burnt  lime 
chemically  considered  is  the  oxide  of  the  metal  calcium,  and 
this  oxide  has  a  great  readiness  to  combine  with  water.  A 
great  deal  of  heat  is  produced  in  this  process,  and  the  oxide 
of  calcium  is  changed  into  hydroxide  of  calcium,  which  is 
slaked  lime.  Slaked  lime  may  be  made  into  a  kind  of  paste 
with  water,  and  a  mixture  of  this  with  sand  forms  ordinary 
mortar.  The  mortar  hardens  completely  between  the  bricks  ; 
in  doing  this  it  combines  with  the  carbonic  acid  of  the  air 
and  again  forms  carbonate  of  lime.  This  reaction  has  led  to 
the  custom  of  burning  baskets  of  coke  in  new  buildings ; 
carbonic  acid  is  produced,  and  thus  the  setting  of  the  mortar 


MORTARS— CEMENTS  2 1 1 

is  hastened.  In  the  course  of  centuries  the  sand  in  the 
mortar,  which  chemically  looked  at  is  silicic  acid,  also  takes  a 
part  in  the  setting  process  by  gradually  forming  silicate  of 
lime,  which  is  an  extremely  hard  substance.  It  is  for  this 
reason  that  old  brick  buildings  are  so  very  solid  ;  it  was  not 
the  ancients  who  made  such  durable  mortars — the  durability 
results  from  age. 

The  hardness  of  silicate  of  lime  has  been  known  for  long, 
but  it  was  not  until  1896  that  a  method  was  found  for  turning 
this  to  practical  account.  Silicate  of  lime  is  formed  very 
slowly  at  ordinary  temperatures,  but  the  formation  of  this 
compound  proceeds  rapidly  when  sand  is  heated  with  slaked 
lime.  On  this  fact  depends  the  manufacture  of  lime-sandstone 
bricks,  which  dates  from  the  year  mentioned.  These  bricks 
are  made  by  pressing  into  moulds  a  mixture  of  sand  and 
slaked  lime,  and  heating  to  above  100°  in  closed  vessels.  The 
bricks  are  of  a  fine  white  colour :  they  are  so  hard,  and  they 
withstand  so  well  the  action  of  air,  water,  and  frost,  that  they 
can  be  used  in  building  in  place  of  bricks  made  by  burning 
clay. 

Ordinary  mortars  cannot  harden  except  by  exposure  to  the 
air,  because  carbonic  acid  is  required  for  the  hardening ;  they 
cannot,  therefore,  be  employed  in  building  under  water, 
because  of  the  absence  of  carbonic  acid.  But  if  certain 
additions  are  made  to  the  constituents  of  mortar — for 
instance,  a  large  quantity  of  silicic  acid  and  alumina — the 
mixture  has  the  property  of  setting  to  a  hard  mass  under 
water.  Mortars  of  this  kind  are  called  cements.  Such 
mortars  were  known  in  ancient  times  ;  they  were  probably 
found  out  accidentally,  as  we  know  that  limestones  are  often 
found  containing  large  quantities  of  alumina,  and  such  lime- 
stones form  hydraulic  mortars. 

To  meet   the   enormous   demand   for   cements   nowadays 


212  CHEMISTRY   IN   DAILY  LIFE 

limestone  is  mixed  with  alumina  before  it  is  burnt ;  and  in 
this  way  any  wished-for  quantity  of  cement  can  be  manu- 
factured, and  the  supply  is  independent  of  the  discovery 
of  natural  limestones  containing  alumina.  Another  method 
of  making  cement  uses  the  slag  from  iron  furnaces  (see 
Lecture  XL)  as  raw  material.  The  composition  of  slag 
differs  from  that  of  cement  chiefly  in  that  the  former  contains 
less  lime.  The  slag  is  finely  ground,  mixed  with  limestone, 
and  strongly  heated.  After  grinding  finely,  one  has  cement. 
This  process,  which  is  another  triumph  of  the  technical 
use  of  what  was  a  refuse  substance,  has  been  practised 
since  1890. 

The  main  constituent  of  all  clays,  to  which  we  now  return, 
in  a  chemical  sense,  is  silicate  of  alumina.  Pure  silicate  of 
alumina  is  infusible  in  an  open  furnace  ;  but  its  fusibility  is 
much  increased  by  the  admixture  of  sand  (silicic  acid),  lime, 
potash,  and  oxide  of  iron.  The  manufacture  of  glass  teaches 
us  that  silicates  of  potash  and  lime,  and  also  silicate  of  iron, 
can  be  melted  to  a  glass.  These  constituents  of  clay  melt 
when  the  clay  is  burnt,  the  brick  sinters,  and  the  semi- 
liquefied  particles  of  glass  solidify  on  cooling  and  give 
hardness  and  compactness  to  the  bricks. 

If  a  specimen  of  clay  is  very  poor  in  these  constituents 
that  clay  will  withstand  the  fire  ;  the  most  fire-resisting 
bricks  are  made  from  such  clays,  and  these  bricks  are 
used  for  erecting  fireproof  buildings  and  for  other  similar 
purposes.  These  bricks  are  generally  called  fire-clay  bricks. 

The  plasticity  of  clay  allows  of  the  modelling  in  it  of  the 
most  diverse  objects,  so  that  it  is  not  only  such  simple  things 
as  bricks  that  are  made  of  this  material. 

It  is  easy  to  produce  convex  vessels,  and  vessels  of  other 
forms  having  circular  cross  sections,  by  working  clay  on 


GLAZING   POTTERY  213 

a  rapidly  rotating  wheel.  The  potter's  wheel  has  been 
known  from  very  ancient  times  ;  indeed  it  has  been  in  use 
among  some  peoples — the  Chinese,  for  instance — since  times 
earlier  than  those  of  which  any  written  records  have  come 
down  to  us. 

If  a  vessel  made  on  the  potter's  wheel  is  baked  it  comes  out 
of  the  oven  fairly  hard,  but  porous  like  a  brick,  and  such  a 
vessel  can  scarcely  be  used  for  any  length  of  time  except  as  a 
flower-pot.  If  a  liquid  is  poured  into  a  pot  of  baked  clay  the 
liquid  soaks  into  and  perhaps  through  the  walls  of  the  pot, 
and  the  vessel  cannot  be  properly  cleansed,  and  cannot  be 
used  for  boiling  food,  nor  for  eating  out  of.  To  remedy  this 
state  of  affairs,  articles  made  of  baked  clay  are  glazed — that 
is,  they  are  covered  with  a  glass. 

We  know  that  lead  glass  is  the  most  fusible  kind  of  glass 
(see  p.  206).  The  cheapest  way  of  glazing  pottery  is  there- 
fore to  mix  clay  with  any  suitable  naturally  occurring  lead 
compound,  to  powder  this  mixture  finely,  and  to  cover  the 
article  to  be  glazed  with  the  fine  powder  that  deposits  after 
the  mixture  has  been  stirred  up  with  water.  When  the 
pottery  is  then  placed  in  the  oven,  silicate  of  lead  is  formed 
by  the  combination  of  the  silicic  acid  of  the  clay  with  lead, 
and  being  melted  runs  over  the  surface  of  the  pots  and  forms 
a  glaze  thereon,  so  that  the  pots  are  no  longer  porous  ;  after 
a  single  firing  the  process  is  finished.  Galena  is  the  lead 
compound  most  commonly  used  for  glazing  pottery  ;  it  is 
a  compound  of  lead  and  sulphur,  and  is  found  native  in  many 
parts  of  the  world.  Vessels  glazed  in  this  way  cannot  be 
used  for  cooking,  because  foods  which  contain  acids,  such  as 
those  prepared  with  vinegar,  dissolve  some  of  the  lead,  and 
lead  is  poisonous.  The  sale  of  kitchen  utensils  glazed  with 
lead  glaze  is  therefore  nowadays  forbidden  by  law. 


214  CHEMISTRY  IN   DAILY  LIFE 

Attempts  have  been  made  in  recent  times  so  to  alter  the 
composition  of  these  glazes  as  to  insure  that  the  whole  of  the 
lead  is  so  firmly  combined  with  other  substances  after  firing 
that  none  of  it  can  be  dissolved  by  the  acids  contained  in 
foods,  for  all  cooked  dishes  are  slightly  acid  in  the  strict 
chemical  meaning  of  the  term.  The  results  of  these  attempts 
have  been  successful. 

Stoneware  is  a  much  more  durable  material  than  ordinary 
pottery.  The  clay  used  for  making  stoneware  is  of  such 
a  nature  that  it  melts  superficially  at  a  moderately  high 
temperature,  and  on  cooling  forms  a  hard  mass  which  is 
quite  impervious  to  liquids.  Articles  prepared  in  this  way, 
such  as  the  cheap  grey  or  brownish  bottles  in  which  natural 
seltzer  water  is  sent  out  [in  Germany],  do  not  require  to 
be  glazed  to  make  them  impermeable  by  water. 

But  another  very  simple  method  of  glazing,  which  gives  a 
more  agreeable  and  more  lustrous  surface,  is  also  practised 
with  all  kinds  of  stoneware  goods  that  are  brought  into  the 
market.  When  the  oven  wherein  the  goods  have  been  baked 
has  been  fully  heated,  some  common  salt  is  shaken  into 
the  fire,  and  the  draught  is  shut  off  for  a  time.  The  oven 
gets  filled  with  the  vapour  of  salt,  for  common  salt  is  not 
very  difficult  to  vaporise.  Now  we  know  that  common  salt 
is  a  compound  of  sodium  and  chlorine  ;  the  sodium  coming 
into  contact  with  the  silicic  acid  of  the  clay  on  the  surface 
of  the  vessels  forms  silicate  of  sodium,  and  this  combined 
with  other  silicates — for  clay  consists  essentially  of  silicates 
— forms  a  glass.  To  glaze  the  ordinary  cheap  stoneware 
goods,  it  is  then  sufficient  to  throw  common  salt  into  the 
oven,  and  the  entire  operation  requires  only  a  single  firing. 

Genuine  stoneware  goods,  which  differ  from  pottery  in  that 
they  are  twice  fired,  are  made  by  selecting  a  very  pure  clay, 


GLAZING  STONEWARE  215 

free  from  iron,  and  putting  the  goods  back  into  the  oven  after 
they  have  been  once  fired ;  such  goods  are  quite  white,  and 
the  glaze  they  acquire  is  also  white.  Such  stoneware  hardly 
differs  externally  from  porcelain  ;  but  the  glaze,  which  has 
been  produced  at  a  lower  temperature  than  the  glaze  on 
porcelain,  soon  scratches  when  the  stoneware  is  used,  and 
becomes  covered  with  fine  cracks,  with  the  result  that  the 
vessels  cannot  be  thoroughly  cleaned  and  do  not  look  well ; 
and,  indeed,  stoneware  dishes  are  not  pleasant  for  eating  off 
for  this  reason. 

The  temperature  whereat  the  glaze  is  burnt  into  stoneware 
is  not  very  high,  and  the  custom  is  to  add  some  borax  and 
some  oxide  of  lead  in  order  to  make  a  glaze  that  is  sufficiently 
fusible.  By  properly  choosing  the  mixture  of  lead  oxide  and 
borax  the  lead  becomes  so  closely  combined  that  acids  have 
no  solvent  action  upon  it. 

Stoneware  vessels  become  thoroughly  hard  and  durable  by 
the  first  firing,  as  this  is  sufficient  to  bind  the  whole  mass 
completely  together.  It  is  not  necessary  that  the  material 
should  run  again  while  the  glaze  is  being  burnt  in  by  the 
second  firing ;  and  there  is  therefore  no  danger,  as  there  is 
in  the  case  of  porcelain  (see  forward),  of  the  vessels  getting 
misshapen  and  losing  their  proper  form  during  this  process. 
Hence— and  in  this  these  goods  differ  from  porcelain  (see 
p.  219) — generally  speaking  only  three  depressions  in  the 
surface  glaze  are  noticeable  on  the  bottom  of  a  piece  of  stone- 
ware, which  depressions  mark  the  place  where  the  plate  or 
other  article  was  supported  during  the  burning  in  of  the 
glaze.  The  rim  on  the  undersurface  of  a  porcelain  plate 
is  not  glazed  (see  p.  219). 

Fayence  should  be  spoken  of  in  connection  with  stoneware. 


2l6  CHEMISTRY  IN   DAILY   LIFE 

The  name  of  this  kind  of  clayware  is  derived  from  the  Italian 
town  Faenza,  where  the  ware  was  first  manufactured.  Another 
name  for  the  same  kind  of  ware  is  majolica^  from  the  island 
of  Majorca,  where  goods  of  this  description  were  manufactured 
in  large  quantities  in  olden  times. 

Fayence  requires  a  very  easily  worked,  plastic  clay,  in  order 
that  the  objects — such  as  dishes,  plates,  etc. — may  be  properly 
fashioned,  for  it  is  chiefly  for  carrying  out  ornamentations  in 
relief  that  this  ware  is  used.  Anything  made  in  fayence  is 
pretty  sharply  baked  ;  this  ware  is  therefore  fairly  hard  ;  but 
as  the  clay  is  very  fire-resisting,  the  objects  run  only  slightly 
in  the  ovens,  and  their  outlines  remain  very  sharp.  On  the 
other  hand,  we  know  that  a  clay  which  has  run  but  slightly  in 
the  fire  is  porous ;  hence  \ifayence  ware  is  to  be  impermeable 
by  water  it  must  be  glazed  after  it  has  been  made.  For  this 
reason,  when  the  ware  has  been  once  fired  it  is  covered  with 
some  glazing  material,  and  is  again  passed  through  the  fire. 
Very  various  effects  are  obtained  by  selecting  materials  that 
produce  either  opaque  white  glazes  or  coloured  glazes.  The 
white  opaque  glazes  are  generally  obtained  by  mixing  oxide 
of  tin  with  the  constituents  of  the  ordinary  glazes. 

We  have  now  to  consider  the  most  perfect  of  all  claywares 
— namely,  porcelain. 

Porcelain  possesses  many  of  the  valuable  properties  of  glass 
in  a  more  marked  degree  even  than  glass  itself.  It  is  harder, 
and  bears  changes  of  temperature  without  cracking  better 
than  glass.  On  the  other  hand,  porcelain  cannot  be  worked 
into  so  many  shapes  as  glass  ;  and  one  has  to  be  content 
with  the  pure  whiteness  of  porcelain  in  place  of  the  trans- 
parency of  glass. 

Porcelain  has  been  known  in  China  and  Japan  for  a  very 
long  time.  It  was  discovered  in  Europe  by  the  Saxon  adept 
Bottcher  in  1703.  At  first  he  was  able  to  make  it  only 


PORCELAIN  217 

with  a  brown  colour;  but  in  1710  he  succeeded  in  preparing 
pure  white  porcelain  vessels,  and  these  have  continued  to 
be  made  since  that  year  in  Meissen. 

As  porcelain  must  be  pure  white,  and  as  it  must  be  fired 
at  the  highest  possible  temperature  in  order  to  bring  out  its 
excellent  qualities,  only  such  clays  as  are  quite  free  from  iron 
and  contain  no  fusible  materials  can  be  used  in  the  manu- 
facture. Clay  suitable  for  making  porcelain  is  called  kaolin ; 
such  clay  is  not  very  common.  The  clay  is  purified  by 
shaking  it  with  a  large  quantity  of  water,  whereby  the 
heavier  and  coarser  particles  sink  to  the  bottom,  while  the 
fine  particles  remain  suspended  in  the  water.  The  turbid 
water  is  poured  off  from  the  sediment  into  another  vessel, 
where  it  is  allowed  to  settle.  The  fine  clay  that  is  thus 
obtained  will  scarcely  vitrify  superficially  in  the  furnace, 
and  it  is  therefore  necessary  to  add  some  flux  to  it  before 
shaping  it  into  vessels  which  are  to  be  baked.  The  flux 
which  is  used  for  this  purpose  is  very  finely  ground  and 
washed  potash  felspar,  a  mineral  found  in  nature  which 
melts  and  runs  to  a  glass  at  a  very  high  temperature.  The 
felspars  are  double  compounds  of  silicate  of  alumina  with 
silicate  of  potash  or  soda ;  they  contain  also  some  silicate 
of  lime. 

Vessels  formed  of  a  mixture  of  washed  kaolin  and  felspar 
shrink  so  much  when  they  are  fired  that  they  very  often 
crack  ;  but  this  difficulty  is  overcome  by  adding  silicic  acid 
to  the  other  materials.  Silicic  acid  is  obtained  of  sufficient 
purity  for  this  purpose  by  finely  grinding  and  washing  quartz, 
fireclay,  or  sand.  The  mixture  of  these  three  materials,  to 
which  some  manufacturers  add  a  fourth  material  that  contains 
lime,  is  shaped  on  the  wheel,  like  pottery,  and  the  vessels, 
after  being  dried  (whereupon  they  become  very  fragile), 
are  heated  in  a  furnace  to  a  strong  red  heat,  at  which 


218  CHEMISTRY   IN   DAILY  LIFE 

temperature   they  shrink   and   become   compact   and   fairly 
hard. 

The  porcelain  that  is  prepared  in  this  way  finds  only  one 
application  :  it  is  used  for  the  porous  cells  of  galvanic 
batteries.  If  a  liquid  is  placed  in  a  pot  made  of  this  un- 
glazed  porcelain,  and  the  pot  is  placed  in  another  liquid, 
the  two  liquids  pass  through  the  walls  of  the  pot  and  come 
into  contact,  and  yet  they  do  not  mix,  in  the  ordinary  sense 
of  the  word  mix ;  and  these  are  some  of  the  conditions 
required  for  producing  an  electric  current. 

Porcelain  made  as  described  must  now  be  glazed.  The 
glaze  used  for  porcelain,  unlike  that  employed  for  other 
kinds  of  clayware,  is  extremely  infusible ;  it  forms  a  true 
glass,  which  spreads  over  the  surface  of  the  finished  product. 
The  glaze  consists  of  the  porcelain  material  itself,  with  the 
addition  of  some  more  fusible  substance,  which  makes  the 
melting  of  the  whole  possible.  The  more  fusible  substance 
is  alkali  and  lime,  the  former  being  supplied  by  increasing 
the  quantity  of  felspar. 

The  finely  powdered  and  washed  glazing  substance  is 
stirred  up  with  water  to  a  thin  paste,  and  the  burnt  porcelain 
is  dipped  into  this,  so  that  a  sufficient  quantity  of  the  paste 
adheres  to  the  surface  of  the  porcelain.  The  glazing  paste 
must  be  brushed  off  those  parts  of  the  porcelain  vessel  which 
will  come  into  contact  with  the  supports  whereon  the  vessel 
is  to  rest  in  the  oven,  otherwise  the  vessel  will  be  fused  to 
the  supports  by  the  melting  of  the  glaze.  It  is  for  this 
reason  that  we  always  notice  a  raised  rim  on  the  bottom  of 
a  porcelain  plate,  for  instance,  while  the  bottom  of  a  glass 
dish  is  flat.  Instead  of  removing  the  glaze  from  the  whole 
bottom  of  the  plate  it  is  only  necessary  to  remove  it  from 
the  rim.  The  unglazed  parts  are  rough,  and  get  gradually 
dirty,  because  dirt  slowly  soaks  into  the  pores  and  cannot  be 


GLAZING   PORCELAIN  219 

removed  by  rubbing.  It  is  possible  to  distinguish  genuine 
porcelain  at  a  glance  by  the  presence  of  this  unglazed  rim, 
for  such  a  rim  is  never  found  on  the  under-surface  of  even 
the  best  stoneware  vessels  (see  p.  215). 

In  order  to  melt  the  glaze,  porcelain  goods  are  placed  in 
the  furnace  a  second  time,  and  the  temperature  is  raised  to 
a  point  much  higher  than  that  at  which  stoneware  is  fired. 

We  know  that  stoneware  acquires  its  proper  hardness  by 
a  single  firing,  and  that  the  hardness  is  not  increased  by 
the  process  of  burning  in  the  glaze.  It  is  otherwise  with 
porcelain  ;  the  product  of  the  first  firing,  known  as  "  biscuit," 
is  fairly  hard  and  compact,  but  it  is  only  when  it  has  been 
fired  a  second  time  at  a  very  high  temperature  that  it 
becomes  completely  vitrified.  The  second  firing  is  needed 
to  produce  that  hard  mass,  with  which  the  glaze  is,  so  to 
say,  interfused,  which  is  able  in  so  marked  a  way  to  resist  all 
external  influences.  On  the  other  hand,  the  porcelain  gets 
so  soft  at  this  high  temperature  that  unless  each  piece  is 
supported  at  many  places  on  its  under-surface  it  is  drawn 
quite  out  of  shape  by  its  own  weight. 

The  course  of  the  firing  is  regulated  by  taking  out  single 
trial  pieces  from  time  to  time.  As  the  glaze  gradually  melts 
it  gets  smoother  and  more  lustrous  ;  and  when  it  is  seen  by 
the  transparency  of  the  whole  mass  that  the  biscuit  is 
sufficiently  glazed  the  fire  is  withdrawn,  and  the  oven  and 
its  contents  are  allowed  to  cool  slowly. 

Unglazed  porcelain  may  of  course  be  subjected  to  the 
same  sharp  firing  as  that  by  which  the  glaze  is  burnt  in.  If 
this  is  done  the  whole  shrinks  so  much  that  it  loses  its 
porousness ;  but  the  surface  remains  somewhat  rough,  and 
looks  dull.  Such  ware  is  called  biscuit  porcelain.  It  is  used 
for  making  busts,  statues,  and  similar  objects  which  would  be 
spoilt  by  the  lustre  of  a  glazed  surface. 


220  CHEMISTRY   IN   DAILY   LIFE 

As  regards  the  painting  of  porcelain ,  two  methods  are 
adopted  ;  the  painting  is  done  under,  or  upon,  the  glaze. 

For  painting  under  the  glaze — that  is,  for  painting  the 
strongly  heated  porcelain — only  those  metallic  oxides  can 
be  used — and  there  are  but  few  of  them — which  will  with- 
stand the  very  high  temperature  of  the  second  firing.  One 
has  cobalt  oxide  for  blues,  chromium  oxide  for  greens,  and 
oxide  of  uranium  (one  of  the  rare  elements)  for  black. 

The  advantage  of  this  method  of  painting  is  that  the 
colours  are  indestructible ;  because,  as  they  are  protected  by 
the  glaze,  they  can  be  destroyed  only  by  breaking  the 
porcelain  itself.  While  the  choice  of  colours  for  painting 
under  the  glaze  is  rather  limited,  any  wished-for  shade  of 
colour  may  be  obtained  when  the  painting  is  done  on  the 
glaze.  Hence  any  oil  painting  may  be  copied  on  porcelain. 
This  art  of  porcelain  painting  has  been  cultivated  chiefly  at 
Sevres. 

The  proper  colours,  which  consist,  as  one  would  suppose, 
chiefly  of  metallic  oxides,  are  mixed  with  some  material 
that  readily  melts  to  a  colourless  glaze — lead  oxide,  as  we 
might  suppose,  is  much  used — and,  after  being  mixed  with 
oil,  are  painted  on  to  the  porcelain  ;  and  the  painting  is 
fused  firmly  on  to  the  surface  by  heating  the  piece  in  a 
muffle  furnace.* 

The  gilding  and  ornamenting  in  gold  of  porcelain,  that 
were  so  much  used  in  older  times,  were  carried  out  in  a 
precisely  similar  way.  The  gold,  which  was  burnt  in  with  a 
fusible  substance,  was  dull  when  it  came  from  the  furnace, 
and  required  to  be  polished  in  order  to  make  its  lustre 

*  A  muffle  is  a  kind  of  box  made  of  fireclay  which  is  heated  by  a  fire 
playing  around  it  in  such  a  way  that  the  contents  of  the  muffle  do  not 
come  into  contact  with  the  smoke  nor  with  the  gases  produced  by 
the  fire. 


PHOTOGRAPHY  221 

apparent.  A  gilding  liquid  was,  however,  discovered  in  1830 
— the  gold  being  first  of  all  dissolved  in  aqua  regia  (see 
forward,  Lecture  XL) — which  could  be  painted  on  to  the 
porcelain,  under  proper  conditions,  and,  after  burning,  pro- 
duced a  lustrous  gold-coloured  effect. 


We  cannot  well  enter  upon  an  explanation  of  the 
phenomena  that  come  into  play  in  photography,  which  is  the 
subject  we  now  turn  to,  without  assuming  a  certain  amount 
of  preliminary  knowledge,  because  the  phenomena  in  question 
rest  on  very  complicated  chemical  occurrences. 

In  this,  as  in  other  similar  cases,  we  shall  succeed  best  by 
making  the  historical  development  of  the  subject  the  basis  of 
our  treatment.  By  doing  this  we  see  the  gradual  perfecting 
of  the  subject,  and  we  have  the  opportunity  of  passing  rapidly 
in  our  own  minds  through  the  most  important  stages  of 
thought  which  have  brought  the  art  to  the  high  position  it 
occupies  at  present. 

Silver  dissolves  easily  in  nitric  acid  to  form  a  colourless 
liquid.  When  this  solution  is  evaporated  a  white  salt  is 
obtained.  This  salt  is  called  nitrate  of  silver  \  it  is  also  often 
known  as  lunar  caustic. 

Anything  that  is  rubbed  with  this  salt  soon  becomes  black 
when  exposed  to  daylight.  The  human  skin,  for  instance,  is 
blackened  by  it,  and  lunar  caustic  is  often  used  in  this  way  as 
a  cautery.  If  a  solution  of  the  salt  is  thickened  with  gum, 
and  letters  are  written  with  this  liquid,  the  letters  come  out 
black  after  a  little  time.  Such  writing  can  scarcely  be  re- 
moved, certainly  not  by  washing ;  a  solution  of  lunar  caustic 
therefore  serves  as  an  indelible  ink.  The  reason  of  this 
appearance  is  that  nitrate  of  silver  is  very  ready  to  decompose 


222  CHEMISTRY  IN   DAILY  LIFE 

into  its  two  constituents — the  decomposition  is,  indeed, 
effected  by  exposing  the  salt  to  daylight — and  in  this  decom- 
position the  metal  silver  separates  as  an  extremely  finely 
divided  black  powder. 

This  property  of  the  salt  has  been  known  for  a  long  time ; 
but  it  cannot  be  made  use  of  for  obtaining  pictures,  because 
the  decomposition  is  much  too  slow  for  that  purpose. 

The  preparation  of  pictures  was  first  accomplished  by 
using  certain  salts  of  silver  which  are  much  more  quickly 
changed  by  light  than  the  nitrate  is.  And  the  three  salts 
that  have  been  most  used  in  photography  are  the  chloride,  the 
bromide,  and  the  iodide  of  silver.  These  three  are  all  easily 
prepared.  As  these  salts  are  quite  insoluble  in  water,  they 
are  thrown  down  when  chloride  of  sodium  (common  salt), 
bromide  of  potassium,  and  iodide  of  potassium,  respectively, 
are  added  to  a  solution  of  lunar  caustic.  In  the  case  of 
common  salt,  for  instance,  chloride  of  silver  and  nitrate  of 
sodium  are  produced  ;  thus 

Nitrate  of  silver  4-  chloride  of  sodium  =  chloride  of  silver  +  nitrate  of 

sodium. 

Nitrate  of  sodium  is  known  to  us  as  a  salt  that  is  very 
easily  soluble  in  water  (see  p.  50) ;  hence  it  remains  dissolved 
in  the  water  in  the  foregoing  reaction,  and  therefore  the 
chloride  of  silver  can  be  completely  freed  from  nitrate  of 
sodium  by  washing  with  water. 

Chloride  of  silver  has  been  known  for  long  ;  bromide  and 
iodide  of  silver  have  been  known  since  the  first  quarter  of  the 
nineteenth  century,  at  which  time  bromine  and  iodine  were 
discovered  (see  pp.  46  and  51). 

The  alchemists  made  great  use  of  chloride  of  silver.  It  is 
very  sensitive  to  light,  for  immediately  it  is  exposed  thereto 
its  pure  white  colour  begins  to  change  to  violet,  and  this 


PHOTOGRAPHY  223 

darkens  until  finally  the  colour  becomes  black.  A  physician 
of  Halle  named  Schultze  was  the  first  to  employ  this  salt, 
in  1727,  for  producing  pictures.  He  laid  letters  cut  out  of 
paper  on  a  freshly  made  precipitate  of  chloride  of  silver 
spread  on  a  flat  surface.  Only  the  exposed  parts  became 
darkened,  and  on  removing  the  paper  the  letters  appeared 
white  on  a  dark  background  ;  but  in  a  short  time  the  letters 
also  became  black,  owing  to  the  action  of  the  light.  All  one 
can  say  of  this  experiment  is  that  it  furnished  an  interesting 
observation,  but  that  it  was  not  of  any  practical  utility. 

It  was  not  until  a  hundred  and  twelve  years  after  this  that 
Talbot,  in  1839,  obtained  actual  pictures  by  using  chloride  of 
silver.  His  procedure  was  as  follows.  He  dipped  paper  into 
a  solution  of  common  salt,  and  then  brushed  a  solution  of 
nitrate  of  silver  over  this  paper.  The  paper  now  contained 
chloride  of  silver.  On  the  paper  prepared  in  this  way  he 
laid  a  transparent  "drawing,  and  exposed  the  whole  to  sunlight. 
The  chloride  of  silver  darkened  the  most  in  those  parts  where 
the  greatest  amount  of  light  was  able  to  penetrate  through 
the  transparent  drawing.  Had  Talbot  now  removed  the 
drawing  the  light  would  of  course  have  darkened  the  whole 
of  the  paper — that  is,  Talbot  would  not  have  advanced  on 
what  had  been  done  by  Schultze.  But  the  great  improve- 
ment made  by  Talbot  was  that  he  found  out  a  method  for 
binding,  or  fixing,  the  picture  which  had  been  formed.  He 
took  the  sensitive  paper,  whereon  the  sun  had  produced  an 
image  of  the  drawing,  into  a  darkened  room,  and  there  placed 
it  in  a  boiling  solution  of  common  salt.  Now  chloride  of 
silver  dissolves  in  a  boiling  solution  of  salt.  The  unchanged 
chloride  of  silver  left  on  the  paper  was  thus  removed,  and  the 
drawing  remained  imprinted  on  the  paper,  inasmuch  as 
chloride  of  silver  which  has  been  blackened  by  sunlight  is 


224  CHEMISTRY  IN   DAILY  LIFE 

so  chemically  changed  that  it  is  not  dissolved  by  a  solution 
of  common  salt. 

A  consideration  of  what  has  been  said  will  show  that  the 
picture  obtained  in  the  way  described  must  be  a  negative 
copy  of  the  original  drawing,  for  the  dark  parts  of  the  draw- 
ing let  less  light  through  them  than  the  lighter  parts.  The 
chloride  of  silver  that  was  covered  by  the  darkest  parts  of 
the  drawing  remained  quite  unchanged,  and  was  therefore 
removed  by  the  treatment  with  salt  solution,  so  that  these 
parts  appeared  white,  or  nearly  white,  while  the  parts  covered 
by  the  lighter  portions  of  the  drawing  appeared  dark.  But 
Talbot  now  laid  this  negative  on  paper  made  sensitive  by 
chloride  of  silver,  and,  by  repeating  his  treatment,  obtained 
an  accurate  copy  of  the  original  drawing. 

Talbot's  process  was  evidently  only  a  photographic  method 
of  multiplying  the  original  drawing  ;  but  Daguerre,  also 
towards  the  end  of  the  thirties  of  last  century,  brought 
to  completion  a  method  for  obtaining  pictures  by  means  of 
photography.  Daguerre  is,  therefore,  the  true  discoverer 
of  what  we  now  call  photography.  He  used  the  camera 
obscura  to  obtain  direct  delineations  of  objects,  without 
starting  from  pictures  of  these  objects.  The  camera  obscura 
is  an  apparatus  by  which  pictures  of  objects  placed  in  front 
of  the  instrument  are  produced,  by  the  use  of  lenses,  at  a 
definite  spot  where  a  plate  of  roughened  glass  has  been 
placed  for  the  purpose  of  focussing  the  picture.  In  place 
of  the  plate  of  roughened  glass,  by  the  help  of  which  the 
apparatus  was  sharply  focussed  on  the  object  to  be  photo- 
graphed, Daguerre  put  a  plate  of  silver  on  which  some  iodide 
of  silver  had  been  formed  by  the  action  of  vapour  of  iodine. 
The  photographic  plate  in  the  camera,  in  conjunction  with 
the  lens,  may  be  regarded  as  an  artificial  substitute  for  the 


DAGUERREOTYPES  22$ 

retina  of  the  eye.  What  may  be  called  an  artificial  eye  was 
thus  formed,  which  could  be  extended  in  many  more  ways 
than  human  eyesight.  A  picture  appeared  on  this  plate 
after  the  action  of  light  had  been  allowed  to  continue  for 
about  an  hour  ;  but  Daguerre  had  the  greatest  difficulty  in 
fixing  the  picture,  and  it  was  an  accident  which  first  helped 
him  to  get  over  this  difficulty.  He  noticed  that  when  a  plate 
which  had  been  exposed  to  light  for  a  short  time  only  was 
brought  into  the  vapour  of  mercury  most  of  the  mercury 
was  deposited  on  those  parts  of  the  plate  which  had  been 
most  illuminated,  and  the  picture  stood  out,  so  to  say,  in 
lustrous  mercury.  The  mercury  vapour  developed,  on  the 
silver  plate,  the  picture  yet  invisible  to  the  human  eye. 
Hence  comes  what  seems  to  us  nowadays  the  very  remark- 
able appearance  of  those  old  daguerreotypes,  as  pictures  of  this 
kind  were  called,  which  are  still  to  be  found  in  many  families. 

This  discovery  made  it  possible  to  get  photographic 
representations  of  living  sitters.  To  obtain  the  likeness  of 
a  person  all  that  was  now  necessary  was  that  the  sitter 
should  remain  still  for  a  short  time ;  and  to-day  people  can 
be  photographed  when  in  rapid  motion. 

The  part  of  Daguerre's  discovery  that  must  always  be  of 
most  importance  is  the  following.  Although  the  human  eye 
is  unable  to  perceive  any  change  in  a  sensitive  plate  that 
has  been  exposed  for  a  very  short  time  in  the  camera  obscura, 
nevertheless  the  chemical  action  of  the  rays  of  light  has 
brought  about  a  decomposition  of  the  silver  compounds  on 
the  plate,  and  in  order  to  develope  a  negative  picture  from 
such  a  plate  it  is  not  necessary  to  continue  the  exposure 
until  the  decomposition  is  completed,  but  it  is  sufficient  to 
treat  the  plate  with  a  suitable  reagent,  such  as  vapour  of 
mercury,  which  is  the  only  reagent  of  this  kind  we  have  as 
yet  become  acquainted  with. 
IS 


226  CHEMISTRY   IN   DAILY  LIFE 


An  enormous  sensation  was  caused  by  the  production  of 
pictures  by  a  process  that  was  kept  secret.  After  a  brilliant 
lecture  by  the  physicist  Arago,  the  French  Chamber  of 
Deputies,  in  1839,  voted  a  pension  to  Daguerre  and  his 
coadjutor  Niepce,  on  condition  that  their  process  should  be 
made  public. 

Attempts  began  to  be  made  at  once  to  find  a  substitute 
for  the  expensive  silver  plates  of  the  daguerreotype  process, 
and  Talbot  was  successful  in  using  his  sensitised  paper  in  the 
camera  obscura.  He  sensitised  his  paper  with  iodide  of 
silver  in  place  of  chloride  of  silver  by  drawing  it  through 
a  solution  of  iodide  of  potassium  after  it  had  been  soaked  in 
a  silver  solution. 

Talbot  now  made  use  of  a  solution  of  hyposulphite  of  soda, 
in  place  of  a  boiling  solution  of  sodium  chloride,  for  dis- 
solving the  unchanged  iodide  of  silver  that  remained  on  the 
paper  after  exposure  ;  this  salt  dissolves  chloride  of  silver,  as 
well  as  bromide  and  iodide  of  silver,  very  easily  in  the  cold, 
and  it  is  now  always  employed  for  the  purpose  for  which 
Talbot  used  it.  But  the  roughness  of  even  the  best  paper 
made  itself  unpleasantly  apparent  in  Talbot's  process,  and  it 
seemed  as  if  the  pictures  produced  by  Daguerre's  method 
on  polished  silver  plates  would  gain  the  victory.  Matters 
were,  however,  altered  by  Nie"pce's  introduction  into  photo- 
graphy of  solutions  of  albumen.  If  iodide  of  potassium  is 
added  to  a  solution  of  albumen,  and  this  liquid  is  poured 
on  to  glass  plates,  which  are  then  dried,  and  afterwards  dipped 
into  a  solution  of  nitrate  of  silver,  a  perfectly  smooth  film  of 
albumen  is  formed  on  the  glass,  and  this  film  is  sensitive  to 
light  because  of  the  iodide  of  silver  which  it  contains;  more- 
over, this  film  has  none  of  the  roughness  of  paper,  and  it  is 
capable  of  yielding  excellent  pictures, 


DEVELOPERS  22/ 

The  pictures  produced  in  the  camera  obscura  are  negatives, 
and  they  must  therefore  be  transferred  to  sensitised  paper, 
as  was  originally  done  by  Talbot,  to  produce  positives — that 
is,  true  representations  of  the  objects  photographed.  From 
this  time  onwards  the  paper  to  which  the  negative  was  to 
be  transferred  was  covered  with  a  sensitised  film  of  albumen, 
and  very  finished  results  were  obtained  because  of  the  smooth- 
ness of  the  surface  and  the  consequent  brilliancy  of  the 
picture  produced  thereon.  But  solutions  of  albumen  have 
an  unpleasant  readiness  to  putrefy  ;  this  led  to  the  substitution 
of  collodion  for  albumen,  as  recommended  by  Fry.  Collodion  * 
is  a  solution  of  nitrated  cotton  wool,  that  is  guncotton 
(see  p.  125),  in  a  mixture  of  ether  and  alcohol. 

The  invisible  change  that  is  brought  about  by  a  brief 
exposure  to  light,  which  Daguerre  had  succeeded  in  fixing  by 
means  of  vapour  of  mercury,  must  and  can  be  fixed,  as  we 
have  already  mentioned,  on  those  plates  which  are  used  in 
place  of  the  silver  plates  of  Daguerre.  The  substances  that 
are  employed  for  doing  this  are  classed  together  under  the 
name  of  developers.  The  developers  that  were  used  in  the 
earlier  days  of  photography  were/errous  sulphate  (commonly 
known  as  green  vitriol)  and  pyrogallic  acid.  All  sorts  of 
chemical  substances  have  been  tried  from  time  to  time  ; 
of  these  hydroquinone  has  been  found  to  answer  especially 
well. 

In  the  collodion  process,  which  we  shall  now  consider,  a 
glass  plate  is  covered  with  collodion  mixed  with  bromide 
and  iodide  of  potassium,  and  is  dipped  into  a  solution  of 
nitrate  of  silver  ;  the  wet  plate,  which  contains  both  bromide 
and  iodide  of  silver  along  with  some  adhering  nitrate  of 
silver,  is  then  exposed  in  the  camera.  If  the  plate  is  brought, 

*  This  substance  was  first  employed,  by  Maynard,  as  a  glue  ;  hence 
the  name  collodion,  from  xdXXij  =  glue. 


228  CHEMISTRY   IN    DAILY   LIFE 

after  exposure,  into  a  solution  of  green  vitriol  or  pyrogallic 
acid  (in  the  dark  room),  this  reagent  reduces  the  excess  of 
silver  nitrate  to  silver,  but  it  does  not  act  on  the  bromide  or 
iodide  of  silver  on  the  plate.  The  silver  which  is  thus 
separated  from  the  nitrate  of  silver  as  a  fine  powder  deposits 
itself  on  those  parts  of  the  plate  which  have  been  exposed 
to  light,  in  proportion  to  the  amount  of  light  that  reached 
the  different  parts,  just  as  the  vapour  of  mercury  did  in  the 
daguerreotyping  process.  The  result  of  this  procedure  is 
that  the  negative  becomes  visible.  The  fixation  of  the 
negative,  and  the  removal  of  the  excess  of  bromide  and 
iodide  of  silver,  is  brought  about  by  immersing  the  plate  in  a 
solution  of  hyposulphite  of  soda,  which  dissolves  and  so 
removes  the  bromide  and  iodide  of  silver.  The  process  may 
be  called  an  acid  process  in  the  chemical  sense  inasmuch  as 
pyrogallic  acid  is  employed.  Attempts  were  made  to  prepare 
in  this  way  dry  plates  which  might  be  stored  and  used  at 
any  time,  but  without  success. 

In  i860  Russell  found  that  the  effect  of  light  on  the 
precipitate  of  silver  bromide  and  iodide  on  the  plate  contained 
in  the  camera  obscura  could  be  made  visible  without  the 
presence  on  the  plate  of  any  excess  of  silver  nitrate.  If  the 
excess  of  silver  nitrate  is  thoroughly  washed  away  from 
the  wet  plate  by  a  large  quantity  of  water,  and  the  plate, 
after  exposure,  is  immersed  in  an  alkaline  solution  of 
pyrogallic  acid  (that  is,  in  a  solution  prepared  by  adding 
alkali  to  the  pyrogallic  solution  used  in  the  older  process), 
the  alkaline  pyrogallate  acts  upon  the  bromide  and  iodide 
of  silver — this,  we  know,  the  solution  without  addition  of 
alkali  did  not  do — in  proportion  to  the  amount  of  light 
that  has  fallen  upon  the  plate,  and  a  picture  is  produced, 
which  can  be  fixed  by  hyposulphite  of  soda,  which  removes 


GELATIN   EMULSION   PROCESS  22Q 

the  unchanged  bromide  and  iodide  of  silver.  This  discovery 
brought  nearer  the  possibility  of  making  dry  plates,  inas- 
much as  it  was  no  longer  necessary  to  leave  an  excess  of  a 
solution  of  silver  nitrate  on  the  plates. 

It  was  soon  found  that  alkaline  pyrogallate  solution 
acts  much  better  on  bromide  than  on  iodide  of  silver ;  and  it 
is  for  this  reason  that  bromide  of  silver  has  become  so 
important  in  photography. 

Maddox  in  1871  recommended  the  employment  of  gelatin 
in  place  of  collodion  ;  but  the  true  discoverer  of  the  gelatin 
emulsion  process,  which  has  now  gained  complete  supremacy, 
was  Bennett,  in  the  year  1878.  Bennett  showed  that  a  silver 
bromide  gelatin  emulsion  gains  that  high  degree  of  sensitive- 
ness for  which  we  praise  such  emulsions  to-day  only  after 
prolonged  warming.  The  preparation  of  the  dry  plates  that 
are  used  to-day  is  based  on  the  employment  of  gelatin  and 
on  the  observation  made  by  Bennett  ;  the  process  is  as 
follows. 

Bromide  of  ammonium  (in  place  of  the  bromide  of 
potassium  formerly  used)  is  dissolved  in  water,  in  a  dark  room, 
and  gelatin  and  then  nitrate  of  silver  are  added,  the  tempera- 
ture being  at  first  kept  at  75°  C.  [167°  R],  but  afterwards 
raised  to  boiling  ;  bromide  of  silver  is  thus  formed.  Every- 
thing that  will  dissolve  in  water  is  washed  out  of  the  silver 
bromide  gelatin  emulsion  thus  produced  ;  the  emulsion  goes 
solid  on  cooling;  after  washing,  it  is  liquefied  by  heating, 
and  poured  on  to  glass  plates,  which  are  dried  as  quickly 
as  possible  in  drying  racks,  and  are  then  ready  to  be  sent 
into  the  market.  They  are  packed  in  a  dark  room,  in  such  a 
way  that  it  is  impossible  for  light  to  get  at  them  until  they 
are  used  in  the  camera.  The  plates  prepared  in  this  way 
are  about  ten  times  more  sensitive  than  the  old-fashioned  wet 
collodion  plates. 


230  CHEMISTRY   IN    DAILY   LIFE 

The  great  development  of  amateur  photography  began  with 
the  manufacture  of  these  plates.  The  preparation  of  sensitised 
plates,  which  up  to  that  time  had  been  the  most  difficult 
operation  in  photography,  was  taken  away  from  the  photo- 
grapher and  relegated  to  the  manufacturer. 

Excellent  pictures  are  readily  obtained  by  the  use  of  dry 
plates  provided  the  camera  is  furnished  with  good,  and 
therefore  expensive,  lenses ;  and  the  exposure  need  not 
exceed  a  second,  so  great  is  the  sensitiveness  of  these  plates. 
The  decomposition  of  the  bromide  of  silver  which  is  started 
at  those  parts  of  the  plate  whereon  the  light  has  fallen,  and 
which  is  too  slight  to  be  detected  by  the  human  eye,  is  carried 
to  the  desired  extent  by  the  developer.  As  soon  as  it  is 
seen,  by  examining  the  plate  in  the  red  light  (see  forward) 
of  the  dark  room,  that  the  development  has  proceeded  far 
enough,  the  bromide  of  silver  which  has  been  unacted  on  is 
removed  by  immersing  the  plate  in  a  solution  of  hyposulphite 
of  soda,  and  the  negative  is  finished.  The  negative  is  then 
transferred  to  sensitised  paper,  and  we  obtain  that  re- 
presentation of  the  original  object  which  is  known  as  a 
photograph. 

The  greatest  inconvenience  for  amateur  photographers  is 
the  need  of  a  dark  room.  Recent  attempts  to  abolish  this 
need  have  been  fairly  successful,  and  it  looks  as  if  it  will 
be  possible  to  produce  photographic  pictures  without  using  a 
dark  room. 

The  whole  art  of  photography  evidently  rests  on  the 
chemical  action  of  light  on  easily  decomposable  salts,  the 
most  important  of  which  are  to-day  the  salts  of  silver.  Now 
the  science  of  physics  tells  us  that  white  light  consists  of 
the  different  colours  which  become  visible  in  the  rainbow. 


PHOTOGRAPHIC  ACTION   OF   DIFFERENT  LIGHTS      231 

If  white  light  is  broken  up  by  means  of  a  prism  into  its 
coloured  constituents,  and  if  attempts  are  made  to  photograph 
the  spectrum  thus  obtained  in  the  ordinary  manner,  it  is 
found  that  scarcely  any  effect  is  produced  on  the  photographic 
plate  by  the  red  rays,  but  that  the  greatest  effect  is  produced 
by  the  rays  at  the  other  end  of  the  spectrum,  that  is,  by  the 
violet  and  the  ultra-violet  rays.  The  ultra-violet  is  that  part 
of  the  spectrum  which  comes  after  the  violet  part ;  it  is  not 
visible  to  the  human  eye,  to  which  it  appears  black,  but  it 
acts  on  the  photographic  plate.  This  behaviour  of  the 
colours  of  the  spectrum  towards  sensitive  plates  explains  why 
the  development  of  the  plate  taken  out  of  the  camera  can  be 
conducted  in  red  light  without  the  plate  being  affected. 

In  the  same  way  it  is  found  that  yellow  and  green  light, 
as  well  as  red  light,  act  only  very  slightly  on  the  plates. 
This  fact,  which  is  very  troublesome  in  attempts  to  reproduce 
oil  paintings  photographically,  makes  itself  apparent  in 
portrait  photography  so  far  as  the  clothing  of  the  sitters  is 
concerned.  For  this  reason  it  is  necessary  to  correct  the 
photographic  pictures  of  coloured  objects,  especially  of 
portraits  ;  the  correcting  process  is  called  retouching. 

Vogel  found  that  this  inconvenience  could  be  avoided  by 
adding  very  small  quantities  of  certain  dyes  to  the  silver 
bromide  gelatin  plates  themselves.  The  plates  are  thus  made 
sensitive  to  colours  which  do  not  affect  plates  that  have  not 
been  subjected  to  this  treatment,  as  the  silver  bromide  on  the 
specially  prepared  plates  is  acted  on  by  light  of  the  same 
colour  as  that  of  the  dyes  which  have  been  added.  It  is  only 
since  that  discovery  that  it  has  become  possible  to  produce 
those  beautiful  photographic  presentments,  especially  of  oil 
paintings,  that  we  are  accustomed  to  see  to-day.  The  older 
photographs,  or  those  produced  with  the  ordinary  dry  plates, 


232  CHEMISTRY   IN   DAILY   LIFE 

show  large  portions  of  the  originals  only  in  a  vague  and 
indefinite  manner.  We  may  therefore  look  on  the  main  part 
of  the  problem  of  reproducing  coloured  objects  photo- 
graphically in  black  in  a  proper  manner  as  solved  by  the  use 
of  orthochromatic  plates. 

But  another  thing  remains  to  be  done,  and  this  is  quite 
different  from  the  problem  we  have  been  considering,  although 
the  two  are  often  confused,  and  that  is  to  produce  photo- 
graphs in  colours.  We  shall  consider  the  solution  of  this 
problem,  which  was  accomplished  in  1907,  after  dealing  with 
pigment  printing. 

Coloured  objects  can  now  be  most  successfully  reproduced 
in  colours  by  a  process  known  as  pigment  printing ;  but  this 
process,  as  its  name  signifies,  is  not  a  purely  photographic 
method. 

The  following  is  the  foundation  of  the  process.  It  has 
already  been  stated  that,  besides  the  sensitive  salts  that  have 
been  enumerated,  there  are  many  mixtures  which  are  sen- 
sitive to  light.  For  instance,  if  a  solution  of  bichromate  of 
potash  is  mixed  with  a  solution  of  gelatin,  and  the  sun  is 
then  allowed  to  shine  upon  any  object  which  has  been  washed 
over  with  this  liquid,  it  is  found  that  the  gelatin,  which  was 
before  soluble,  very  quickly  becomes  insoluble  in  water. 
The  cause  of  this  is  that  the  light  acts  upon  the  bichromate 
of  potash  in  such  a  way  as  to  change  some  of  it  into  an 
oxide  of  chromium,  which  acts  on  the  gelatin  like  a  tanning 
agent  and  produces  insoluble  substances.  We  have  already 
learnt  something  of  the  attempts  that  have  been  made  to 
prepare  chrome  leather  directly  (see  p.  142).  If  then  a 
photographic  negative,  obtained  in  the  ordinary  way,  is  laid 
in  the  dark  on  paper  covered  with  chrome-gelatin,  the  parts 
which  the  light  reaches  will  become  insoluble ;  and  if  the 
unattacked  portions  of  the  chrome-gelatin  are  now  removed 


PIGMENT  POINTING  233 

by  washing  with  water  in  the  dark  room,  a  picture  is  ob- 
tained which  is  not  black,  like  those  formed  when  silver 
paper  is  used,  but  is  nearly  invisible,  because  it  is  merely 
of  the  colour  of  the  gelatin.  But  there  is  no  reason  why 
the  gelatin  should  not  be  coloured  with  a  suitable  pigment 
before  the  process  is  carried  out.  Yellow  gelatin  will  yield 
a  yellow  picture,  red  gelatin  a  red  picture,  and  blue  gelatin 
a  blue  picture ;  and  if  the  three  transparent  delineations  that 
are  thus  obtained  are  fastened  over  one  another — and  they 
must  fit  exactly  each  on  the  other  as  they  are  all  obtained 
from  the  same  negative  on  a  sensitive  plate — the  most  re- 
markable results  are  produced. 

The  theory  of  mixed  colours,  as  developed  by  physicists, 
predicts  that  very  brilliant  results  should  be  obtained  by 
this  method  as  regards  the  true  rendering  of  the  colours  of 
the  original  objects,  and  the  performances  have  nearly  realised 
these  predictions.  Although  the  process  may  appear  from 
the  description  we  have  given  of  it  to  be  very  simple,  yet 
the  difficulties  which  have  to  be  overcome  in  practising  it 
successfully  are  very  great.  The  process  is  often  conducted 
by  taking  three  negatives,  a  red,  a  blue,  and  a  yellow  glass 
plate  being  placed,  successively,  before  the  lens  of  the  camera. 
The  three  negatives  are  then  changed  into  positives ;  and 
these  are  coloured  with  the  same  dyes  as  were  used  for 
making  the  plates  sensitive  (see  p.  231),  and  are  then  printed 
on  one  another. 

There  are  many  other  reproduction  methods,  some  of  them 
actually  in  use,  others  in  the  stage  of  being  tried  ;  but  we 
cannot  go  into  these  methods  now.  They  all  demand  the 
formation  of  a  negative  by  means  of  the  camera — that  is, 
they  all  begin  with  a  representation  of  an  object  by  photo- 
graphic methods,  and  inasmuch  as  they  do  this  they  are 
all  legitimate  children  of  photography. 


234  CHEMISTRY   IN    DAILY   LIFE 

Many  investigators  of  the  first  rank  have  attempted  to 
solve  the  problem  of  producing  photographs  of  coloured 
objects  in  the  true  colours  of  these  objects.  The  brothers 
Lumiere  were  the  first  to  accomplish  this  aim,  in  a  way 
which  is  always  applicable,  in  the  year  1907.  Their  process 
enables  portraits  to  be  taken  in  a  studio  in  20  seconds, 
with  a  clouded  sky ;  and  the  picture  can  be  developed  in  2\ 
minutes  in  the  dark  room.  They  prepare  their  plates  so  that 
two  parts  of  green-coloured  starch  granules  are  intimately 
mixed  with  one  part  of  red-  and  blue-coloured  granules.  The 
colour  of  the  mixture  is  pure  white.  The  mixture  is  distri- 
buted over  the  surface  of  a  glass  plate,  which  has  been  coated 
with  a  sticky  substance,  in  such  a  way  that  no  starch 
granule  is  superimposed  on  another.  The  granules  are 
carefully  smoothed  by  a  press,  so  as  to  form  a  continuous 
layer.  This  light-filtering  layer  is  varnished,  and  a  sensitive 
emulsion  of  silver  bromide  is  spread  over  the  varnish.  When 
the  plate  is  dry  it  is  placed  in  the  camera  in  such  a  position 
that  the  light  which  comes  through  the  lens  must  penetrate 
the  glass  plate  and  the  light  filter  of  starch  granules  before 
it  reaches  the  emulsion  of  silver  bromide.  When  the  plate 
is  subsequently  developed,  a  coloured  photograph  is  obtained 
which  leaves  little  to  be  desired  so  far  as  correct  colouring 
is  concerned.  The  procedure  is  so  simple  that  amateur  photo- 
graphers can  work  it  without  trouble.  German  colour-films 
(not  glass  plates)  have  come  into  the  market  since  1910. 
These  form  a  valuable  addition  to  the  materials  for  making 
coloured  photographs. 

We  cannot  bring  to  a  close  our  consideration  of  the 
photographic  reproduction  of  objects  without  drawing  especial 
attention  to  the  most  striking  advance  in  this  department — 
that,  namely,  connected  with  the  Rontgen  rays — although  that 


GEISSLER   TUBES  235 

advance  belongs  rather  to  physics  than  to  chemistry.  Even  in 
the  first  lecture  we  had  to  make  an  excursion  into  the  domain 
of  physics  in  order  to  gain  clear  notions  about  the  atmosphere. 
We  all  know  that  electric  sparks,  whether  as  lightning 
or  artificially  produced,  pass  from  one  place  to  another  not 
by  a  straight  but  by  a  zigzag  course.  It  is  the  resistance  that 
the  air  opposes  to  the  passage  of  the  sparks  which  produces 
this  effect.  But  if  the  sparks  are  allowed  to  pass  inside  a 
glass  tube  from  which  the  air  has  been  so  completely  pumped 
out  that  the  internal  pressure  does  not  amount  to  more  than 
about  one  thousandth  of  an  atmosphere — wires  having  been 
fused  through  the  glass  at  the  two  ends  of  the  tube  to  serve 
as  the  poles  of  an  electrical  arrangement — then  the  tube  is 
illuminated  throughout  the  whole  of  its  length  when  the 
sparks  pass,  inasmuch  as  the  resistance  of  the  air  scarcely 
comes  into  play.  Wonderfully  beautiful  colour  effects  are 
obtained  by  using  tubes  of  the  kind  described  containing 
very  minute  quantities  of  different  gases,  such  as  hydrogen 
and  oxygen,  which  radiate  light  of  different  colours.  These 
tubes  are  called  Geissler  tubes^  from  the  name  of  the  cele- 
brated glass-blower  Geissler,  who  was  the  first  to  make  them 
in  perfect  condition.  If  the  attenuation  of  the  air  in  such 
tubes  is  carried  so  far  that  the  pressure  does  not  exceed 
one-millionth  of  an  atmosphere,  which  is  much  less  than 
the  pressure  in  the  Geissler  tubes,  other  phenomena  are 
noticed  when  electricity  passes.  The  whole  tube  is  not 
illuminated,  but  bundles  of  rays  proceed  from  that  one  of 
the  poles  which  is  called  the  katJiode>  while  colour  phenomena 
are  scarcely  noticeable  at  the  other  pole,  which  is  known 
as  the  anode.  If  a  vessel  of  the  form  shown  in  fig.  18  is 
substituted  for  a  tube,  the  kathode  rays  do  not  altogether 
pass  to  the  anode,  but  they  proceed  in  straight  lines,  without 
being  influenced  by  the  anode,  and  produce  a  bright  spot 


236  CHEMISTRY  IN   DAILY  LIFE 

where  they  impinge  on  the  walls  of  the  vessel,  and,  at  the 
same  time,  the  kathode  rays  partly  change  into  Rontgen 
rays. 

In  the  year  1895  Rontgen  made  an  investigation  of  the 
kathode  rays  outside  of  the  tube*  wherein  they  were  pro- 
duced, carrying  out  his  research  in  a  darkened  room.  Having 
completely  encased  the  bent  tube  in  black  pasteboard,  he 
placed  a  paper,  over  which  was  spread  a  solution  of  platino- 
cyanide  of  barium,  in  such  a  position  that  if  the  kathode  rays 
were  produced  they  would  strike  upon  this  paper,  and  he 
noticed  that  the  paper  began  to  fluoresce,  with  a  yellow 
colour,  and  therefore  to  become  visible  in  the  darkened  room. 
Here  then  he  had  to  deal  with  a  new  and  most  interesting 
kind  of  rays,  very  different  from  those  ordinarily  visible  to 
the  human  eye,  and  capable  of  passing  through  a  covering 
of  black  pasteboard.  The  existence  was  revealed  of  rays 
which  the  human  eye  cannot  see  directly,  but  only  in 
the  form  of  fluorescence-phenomena  produced  by  them, 
and  which  act  through  a  black  covering  that  stops  the 
kathode  rays. 

By  fluorescence  is  signified  the  property  which  many  sub- 
stances possess,  among  these  being  platinocyanide  of  barium, 
of  converting  the  ultra-violet  rays  (which  we  have  already 
mentioned)  into  visible  rays  of  light ;  the  greenish  sheen  that 
is  noticed  in  most  kinds  of  petroleum,  for  instance,  is  due  to 
fluorescence.  The  Rontgen  rays  resemble  the  ultra-violet 
rays  contained  in  ordinary  light  in  that  they  occasion 
fluorescence.  The  fluorescence  of  the  paper  we  have  spoken 
of  must  have  been  the  effect  of  some  cause  having  its  origin 
in  the  tube,  which  was  completely  covered,  wherein  the 

*  Rontgen  at  first  used  tubes  of  the  form  shown  in  fig.  18.  Although 
many  modifications  have  been  made  in  the  form  of  the  tubes,  the  oldest 
form  is  retained  here,  inasmuch  as  the  principle  has  not  been  altered, 


RONTGEN   RAYS  237 

kathode  rays  were  produced.  It  must  be  due  to  some  kind 
of  rays  which  are  produced  along  with  the  kathode  rays, 
but  differ  from  these  rays  ;  which  are  not  perceived  by  our 
eyes  ;  which  differ  from  all  rays  previously  known,  in  their 
power  of  passing  through  black  pasteboard.  It  was  also  found 
that  a  book  or  a  wooden  board  placed  in  the  produced 
direction  of  the  kathode  rays  did  not  stop  the  fluorescence 
of  the  barium  platinocyanide  paper  when  that  was  held  on 
the  other  side  of  the  obstruction  ;  hence  the  rays  are  capable 
of  passing  directly  through  such  things  as  a  book  or  a  piece 
of  wood. 

Rontgen  placed  a  sensitised  photographic  dry  plate  in  the 


Direction  of  the  Kathode 
Rontgen  Rays. 


place  where  the  paper  had  been,  and  he  found  that  this 
plate  was  acted  on,  in  a  completely  darkened  room,  by  the 
rays  that  are  invisible  to  the  eye  ;  moreover,  when  he  brought 
various  substances  more  solid  than  paper  or  wood  between 
the  plate  and  the  tube  wherein  the  rays  were  produced, 
shadow  pictures  of  these  substances  were  obtained  on  the 
plate  when  that  had  been  developed  in  the  usual  way. 

Inasmuch  as  the  rays  pass  through  relatively  soft  flesh  but 
not  through  much  more  compact  bones,  a  shadow  picture 
of  the  bony  skeleton  of  the  hand  is  obtained  by  exposing 
the  hand  to  the  action  of  these  rays. 

Photographs  can  be  taken  with  the  Rontgen  rays  in 
ordinary  daylight,  for  it  is  only  necessary  to  place  the 


238  CHEMISTRY  IN   DAILY  LIFE 


sensitised  plate  in  a  black  box,  and  to  lay  the  object — the 
hand,  for  instance — on  the  top  of  this  box  while  the  rays  are 
allowed  to  fall  on  to  the  object ;  the  rays  pass  through  the 
wood,  which,  however,  protects  the  plate  from  daylight,  on 
to  the  plate  inside.  These  rays  are  not  refracted  by  lenses  ; 
hence  pictures  obtained  by  their  use  are  true  and  accurate 
shadow  pictures  of  the  same  size  as  the  original  objects,  in 
distinction  to  photographs  proper,  which  permit  of  the 
representation  of  a  large  landscape  on  a  space  not  more  than 
one  or  two  inches  square  because  ordinary  light  is  refracted 
in  passing  through  lenses. 

The  Rontgen  rays  act  on  sensitive  silver  salts,  but  much 
more  slowly  than  ordinary  light ;  but,  to  put  the  matter 
shortly,  they  are  not  ultra-violet  nor  ultra-red  rays,  because 
they  are  not  refracted  by  lenses  or  prisms,  as  ordinary  light 
is  ;  they  are  not  light  in  the  ordinary  sense  of  the  word, 
because  we  cannot  see  them  ;  they  are  not  kathode  rays, 
because  we  see  these  illuminating  the  tube  through  which 
they  pass ;  a  part  of  the  kathode  rays  is  changed  into 
Rontgen  rays  by  impinging  on  the  glass  wall  of  the  vessel. 
They  are  something  altogether  new ;  and  what  is  to  be  the 
value  of  this  new  thing,  whether  for  science  or  for  ordinary 
life,  we  must  learn  fully  at  a  later  time. 

These  rays  have  already  proved  so  useful  in  surgery  that 
the  means  of  producing  them  has  become  a  necessary  part  of 
the  surgeon's  apparatus  for  detecting  fractures  in  bones,  the 
presence  of  foreign  substances,  etc.  The  rays  are  also  used 
as  a  curative  agent  in  some  cutaneous  diseases. 

In  1896  Becquerel  set  himself  to  discover  whether  an 
inversion  of  the  phenomena  of  the  Rontgen  rays  was  possible  ; 
that  is,  considering  that  these  rays  produce  fluorescence, 
whether  fluorescent  substances  could  produce  Rontgen  rays. 
He  placed  different  fluorescent  substances  on  photographic 


RADIUM  239 

plates  which  were  shielded  from  the  action  of  ordinary  light. 
On  developing  the  plates,  he  found  that  many  compounds 
of  the  element  uranium  had  impressed  their  photographic 
images  on  the  plates,  through  the  black  paper.  The  com- 
pounds of  uranium  had  emitted  rays  unrecognised  until  then. 
These  rays  showed  themselves  to  be  different  from  Rontgen 
rays,  for  instance,  in  that  on  taking  a  photograph  of  the  hand, 
an  outline  appeared  of  the  whole  hand,  but  the  bones  were 
not  visible.  Thereupon  the  search  began  for  substances 
which  acted  like  uranium  compounds,  for  radio-active  sub- 
stances. The  mineral  pitchblende  found  in  Joachim's  Valley 
in  Bohemia  was  found  to  possess  this  property.  This  mineral 
contains  many  chemical  elements  ;  investigation  showed  that 
the  radio-activity  of  pitchblende  was  connected  with  the  pre- 
sence in  it  of  barium.  It  has  been  found  possible  to  decompose 
the  radio-active  constituent  and  to  obtain  a  substance  more 
radio-active  than  any  previously  known ;  this  substance  was 
named  radium  by  its  discoverer,  Curie.  One  gram  [30  grains] 
of  radium  chloride — which  is  the  compound  that  comes  on 
to  the  market — costs  about  ;£  16,000;  it  is  sold  by  the 
milligram.  Hence  one  can  have  a  notion  of  the  labour 
needed  to  extract  from  pitchblende  the  minute  quantities 
of  radium  that  are  found  in  that  mineral. 

The  more  minute  investigation  of  radium  soon  revealed 
such  remarkable  properties,  so  different  from  those  which 
belong  to  any  substance  known  to  science,  that  the  behaviour 
of  radium  seemed  for  a  time  to  be  inexplicable.  All  the 
ordinary  methods  of  investigation  and  the  ordinary  theories 
seemed  to  be  inapplicable.  The  most  astonishing  thing  about 
radium  is  that  it  is  constantly  undergoing  change,  and 
sending  out  rays  of  a  very  extraordinary  character.  The 
name  emanation  has  been  given  to  these  rays.  Inasmuch 
as  the  emanation  of  radium  has  been  obtained  in  the  form 


240  CHEMISTRY  IN   DAILY  LIFE 

of  a  liquid,  it  is  evident  that  the  emanation  is  not  really  a 
collection  of  rays,  but  has  something  material  about  it.  One 
may  speak  of  it  as  a  stream,  as  one  speaks  of  a  stream  of 
water.  Radium  emanation  is  found  in  all  those  springs  of 
water  which  long  experience  has  shown  to  possess  healing 
properties,  which  properties  cannot  be  connected  with  any 
other  of  their  chemical  constituents.  The  secret  of  the 
springs  at  Gastein,  Baden-Baden,  Kreuznach,  and  elsewhere 
[including  those  at  Bath]  is  thus  elucidated  ;  and  a  reason 
is  found  for  the  fact  that  these  waters  are  efficacious  only 
when  used  at  their  sources.  For  the  emanation  is  very 
mutable,  and  disappears  from  the  waters  after  a  short  time. 
An  apparatus  is  now  to  be  found  in  druggists'  shops,  the 
radium-containing  material  of  which  gives  off  emanation  to 
water  stored  therein,  so  that  water  charged  with  the  emana- 
tion can  be  drunk  in  these  shops.  The  aggregate  rays 
given  off  by  radium  exert  a  very  marked  and  directly 
destructive  action  on  the  skin  ;  nevertheless,  they  are  useful 
as  a  curative  agent  in  certain  skin  diseases. 


LECTURE  XI 

Noble  and  base  metals — Ores — Gold — Platinum — Potassium  cyanide — 
Silver — Relations  of  value  between  gold  and  silver — Bimetallism 
— Gold  currency — Reduction  of  metallic  oxides — Roasting  sulphur 
compounds —  Pig  iron  —  Steel  —  Wrought  iron — Blast  furnaces- 
Slags  —  Coke  —  Puddling  —  Rolled  iron  —  Railways — Cementation 
steel — Cast  steel — Bessemer  steel — Spiegeleisen — Manganese — De- 
phosphorising iron — Soft  steel — Nickel  steel — Chromium  steel — Gas 
furnaces — Regenerative  furnaces — Open  flame  furnaces — Zinc — 
Electro-deposition  of  metals — Potassium — Sodium — Aluminium. 

WE  are  accustomed  to  speak  of  two  great  classes  of  metals, 
the  noble  and  the  base  metals.  The  chief  difference  between 
these  classes  is  that  the  noble  metals  are  very  slightly  acted 
on  by  other  elements,  especially  by  oxygen  and  sulphur, 
which  are  most  frequently  taken  into  consideration  because 
of  their  abundant  distribution  on  the  earth's  surface,  whereas 
the  base  metals  soon  succumb  to  the  attack  of  other  elements, 
or,  to  express  it  otherwise,  very  readily  enter  into  chemical 
combination  with  other  elements.  The  noble  metals,  as  we 
should  expect,  generally  occur  uncombined  in  the  earth, 
and  they  are  therefore  relatively  easily  obtained  from  their 
deposits  ;  whereas  the  other  metals  have  been  converted  in 
the  course  of  endless  ages  into  oxides  by  the  action  of  oxygen, 
or  into  sulphides  by  the  action  of  sulphur,  or  they  occur  in 
the  form  of  yet  more  complicated  combinations.* 

*  Miners  call  the  sulphur  compounds  of  metals  sometimes  pyrites, 
sometimes  glances^  and  sometimes  blendes.  The  first  two  have  a  metallic 
habit— lead  glance,  for  instance  ;  the  last— zincblende,  for  instance- 
has  not. 

1 6  24' 


242  CHEMISTRY  IN   DAILY  LIFE 

That  the  base  metals  may  become  serviceable  to  mankind 
they  must  be  separated  by  some  means  or  other  from  the 
substances  that  mask  them.  The  naturally  occurring  com- 
pounds of  such  elements  are  spoken  of  as  the  ores  of  the 
metals,  when  these  are  found  in  any  spot  in  quantities 
sufficient  to  make  the  technical  extraction  of  the  metals 
therefrom  profitable. 

It  is  only  in  poetry  that  the  word  ore  is  used  as  synonymous 
with  metal ;  in  practical  affairs  it  is  always  taken  to  mean, 
not  the  metal  itself,  but  any  compound  of  a  metal  which  is 
found  in  nature. 

It  would  be  of  little  use  for  us  to  speak  of  all  the  metals 
in  this  place.  In  addition  to  certain  points  connected  with 
the  noble  metals,  we  shall  deal  in  detail  only  with  the 
preparation  of  iron,  which  is  the  most  important  metal  in 
ordinary  life.  And  in  doing  this  we  shall  be  able  to  gain 
some  .insight  into  the  extraction  of  metals  generally. 

Gold  and  platinum^  which  are  noble  metals  in  the  chemical 
sense,  occur  almost  solely  uncombined  in  the  earth.  Gold 
and  platinum  also  are  found  in  the  sands  of  rivers,  or  in 
other  deposits  of  sand,  and  they  are  obtained  by  washing 
these  sands.  When  gold  is  found  imbedded  in  hard  rocks 
these  are  stamped  and  ground,  and  the  metal  is  extracted 
either  directly  by  washing  with  water,  or  by  the  help  of 
mercury  or  potassium  cyanide,  which  dissolve  gold. 

In  South  Africa,  for  instance,  the  gold-bearing  rock — 
which  contains  about  40  to  50  grams  of  gold  (worth  £2  to 
£2  ioj.)  in  1,000  kilograms,  equal  to  about  only  0-002  per 
cent,  of  gold — was  at  first  stamped,  with  addition  of  water 
and  mercury.  The  mercury  dissolved  the  gold  ;  the  amalgam 
was  distilled,  whereby  the  mercury  was  removed,  and  the 
gold  remained  in  the  retorts.  A  considerable  quantity  of 


EXTRACTION   OF  GOLD  AND  SILVER  243 

gold,  however,  remained  in  the  crushed  rock.  In  the  nineties 
of  last  century  Forest  introduced  the  method  of  lixiviating 
the  residue  with  a  solution  of  potassium  cyanide,  which 
removed  almost  the  whole  of  the  gold.  The  residual  crushed 
rock  is  placed  in  vats,  made  of  cement,  holding  about  400,000 
litres  [about  90,000  gallons]  and  covered  with  a  dilute 
solution  of  potassium  cyanide ;  air  is  driven  through  the 
liquid  (the  oxidising  action  of  air  is  needed  for  the  reaction), 
and  the  gold  is  dissolved.  Zinc  which  contains  lead  is 
placed  in  the  solution  drawn  off  from  the  residual  solid 
matter,  and  as  this  goes  into  solution  the  gold  is  precipitated. 
This  process  proved  itself  to  be  so  successful  that  it  is  now 
used  in  many  places  for  the  treatment  of  gold-bearing  rocks 
which  are  so  poor  in  gold  that  the  extraction  of  gold  from 
them  could  not  be  made  remunerative  by  any  other  process. 
Without  doubt  the  cyanide  process  is  the  greatest  advance 
that  has  yet  been  made  in  the  gold  industry  ;  it  has  done 
much  to  bring  about  the  great  increase  which  there  has 
been  in  the  output  of  gold. 

The  extraction  of  silver,  except  in  those  places  where  it 
occurs  native,  is  by  no  means  so  simple  that  it  can  be 
clearly  set  forth  here  ;  we  shall  not  therefore  go  into  the 
methods,  which  are  moreover  all  special  methods  for  this 
metal,  notwithstanding  that  the  chemical  improvements 
made  in  these  processes  have  very  largely  contributed  to  the 
sudden  fall  in  the  price  of  this  metal.  It  will  be  of  more 
interest  for  us  at  present  to  pay  some  attention  to  the 
question  of  the  relative  values  of  the  two  metals,  gold  and 
silver. 

The  oldest  tidings  that  we  have  on  this  matter  come  to 
us  from  about  seven  hundred  and  ten  years  before  Christ. 
A  plate  of  gold  and  a  plate  of  silver  have  been  found  in  the 


244  CHEMISTRY  IN   DAILY  LIFE 

foundations  of  the  palace  of  King  Sargon,  who  flourished 
about  that  time  in  the  Assyrian  city  of  Khorsabad,  and 
these  plates  bear  inscriptions  that  I  Ib.  of  gold  was  worth 
13  J  Ibs.  of  silver  in  those  days.  It  is  very  remarkable  that 
this  relation  of  values  is  found  to  be  approximately  main- 
tained at  all  later  times — for  instance,  in  ancient  Rome  and 
also  during  the  Middle  Ages.  The  exact  relation  between 
the  values  of  the  two  metals  is  known  from  1687  onwards, 
because  the  merchants  of  the  London  and  Hamburg  ex- 
changes have  continued  to  record  this  relation  since  that 
year. 

We  find  that  the  relation  between  the  two  metals  fluctuated 
only  very  slightly  until  the  year  1874;  putting  the  figures 
into  weights,  I  Ib.  of  gold  was  able  to  purchase,  on  the 
whole,  as  much  as  15!  Ibs.  of  silver.  But  matters  changed 
in  1874.  The  enormous  output  of  silver  from  America, 
which  seemed  for  a  time  as  if  it  would  be  exceeded,  if 
that  be  possible,  by  the  supply  coming  from  Australia, 
threw  such  quantities  of  the  white  metal  on  the  market 
that  the  supply  far  exceeded  the  demand. 

It  does  not  much  matter  whether  in  such  a  state  of  affairs 
one  has  to  deal  with  a  white  metal  or  a  red  metal — the 
price  of  copper,  for  instance,  has  been  affected  like  that 
of  silver  by  over-production — or  with  grain,  whatever  is 
thrust  on  to  the  market  must  be  allowed  to  go  at  a  lower 
price ;  and  so  we  find  that  the  enormous  increase  in  the 
production  of  silver,  without  a  corresponding  increase  in 
the  demand,  has  caused  the  price  of  this  metal  to  fall 
gradually.  When  silver  was  cheapest,  it  was  possible  to 
get  37  Ibs.  of  silver  for  I  Ib.  of  gold. 

The  relations  between  gold  and  silver  are  affected  in  the 
way  we  have  described  when  these  metals  are  regarded  as 
commodities,  for  these  relations  are  influenced  by  the  same 


VALUE-RELATIONS   OF   GOLD  AND  SILVER  245 

causes  as  those  which  at  any  time  and  place  influence  the 
relative  values  of  commodities  in  general. 

The  total  amount  of  gold  produced  between  the  years  1492,  that  is, 
from  the  discovery  of  America,  and  1900  was  37,231,900  Ibs.  Troy  ;  and 
the  total  amount  of  silver  produced  in  that  period  was  697,048,168  Ibs. 
Troy  (260,092,600  kilos.).  The  more  exact  numbers  for  the  last  40  years 
are  as  follows  : 

Years.  Gold.  Silver. 

1871-75  ...         463,908  Ibs.  Troy.  ...         5,253,550  Ibs.  Troy. 

1881-85  ...         397,8i9        ,,  .-         7,633,765 

1891-95  ...         654,027        „  ...  12,074,755 

1901-5  ...  1,367,496        „  ...  14,124,296 


Year. 

1906  ...   1,620,957  „  ...    13,786,147 

1907  ...   1,655,564  „  ...    I5,503,l8l 

1908  ...      1,729,028  „  ...  -)     not  yet 

1909  ...      1,806,837  „  ...  >     known 

1910  ...      1,825,080  „  ...  J  accurately 

i  kilo.  (2-68  Ibs.  Troy)  of  gold  is  worth  £139  IQJ.,  and  I  kilo,  of  silver 

about  ^3  i2s.  at  present. 


But  the  relations  between  gold  and  silver  become  much 
more  complicated  when  one  considers  the  money  that  is 
coined  from  the  two  metals.  We  shall  refer  to  the  com- 
positions of  coins  in  Lecture  XII.  when  we  are  dealing 
with  alloys. 

The  Greeks  and  Romans  had  on  the  whole  as  much  gold 
as  they  needed  for  their  coinage.  There  are  no  direct 
complaints  of  the  shortage  of  gold  to  be  found  in  their 
writings.  But  the  wanderings  of  peoples  which  destroyed 
the  culture  of  the  ancient  world,  from  about  the  year  375  A.D., 
and  brought  the  mining  industry  everywhere  to  grief,  so 
affected  the  supply  of  gold  that  a  great  scarcity  of  this 
metal  made  itself  felt.  This  scarcity  of  gold  was  the 
cause  of  the  rise  of  alchemy  ;  this  it  was  that  spurred  on 
human  activity  to  the  endeavour  to  make  gold  artificially, 


246  CHEMISTRY   IN   DAILY  LIFE 

in  order  to  obtain  the  most  convenient  mediums  of  exchange 
for  all  commodities,  and  the  most  convenient  basis  for 
commercial  transactions.  The  aim  of  the  alchemists  was 
not  attained  ;  gold  cannot  be  made  artificially.  The  vast 
amount  of  work  which  was  expended  in  the  quest  led  to 
the  accumulation  of  much  chemical  knowledge,  from  which 
chemistry  at  last  emerged  as  a  science.  In  the  great  empire 
established  by  Charles  the  Great,  about  800,  political  relations 
were  again  made  so  stable  that  a  general  demand  arose  for 
a  coinage  which  should  be  current  everywhere.  As  gold 
could  not  be  obtained  in  sufficient  quantity,  the  only  avail- 
able metal  was  silver.  Charles  the  Great  issued  an  edict 
concerning  coinage,  based  on  silver  as  a  standard.  The 
pound  (libera}  of  silver  was  divided  into  20  parts,  each 
of  which  was  called  a  solidus  (shilling).  Each  solidus  was 
subdivided  into  12  parts,  called  denar  (pence).  This  is  the 
coinage  system  used  in  England  to-day.  The  difference 
is  that  one  pound  sterling  is  now  worth  [20  shillings] 
about  20  marks,  while  a  pound  of  silver  was  worth  about 
[80  shillings]  160  marks  from  the  time  of  Charles  the  Great 
until  about  40  years  ago.  The  reason  for  this  downward 
movement  in  the  value  of  a  pound  sterling  is  simply  the 
fact  that  the  English  kings  debased  the  value  of  their 
coinage,  in  the  Middle  Ages,  when  there  was  a  great  demand 
for  money. 

The  French  kings  carried  the  debasing  of  coinage  further 
than  the  English.  At  the  beginning  of  the  Revolution  they 
had  reduced  the  livre  (libera)  to  the  value  of  4  marks.  The 
Italian  lira  is  worth  to-day  only  about  80  pfennings  [8  pence]. 

Gold  money  was  first  again  coined  in  Europe  in  Pisa, 
Genoa,  Venice,  and  other  city-states  of  Northern  Italy. 
The  extensive  trade  between  these  states  and  Asia  Minor, 
especially  the  Levant,  gradually  brought  them  so  much  gold 


BIMETALLISM  247 

that  their  mints  became  a  remunerative  business.  Florence 
made  a  beginning  in  1252.  Hence  the  designation  of  gold 
coins  as  Floreni^  or  Fiorini.  The  name  Ducat  came  in  some- 
what later;  the  word  comes  from  the  Italian  title  Duca 
(duke).  Gold  coins  were  also  called  Zechins  [or  Sequins} 
from  Zetca,  Italian  for  the  mint. 

As  long  as  the  ratio  between  gold  and  silver  remained  as 
good  as  constant — and  so  far  as  those  who  are  now  living  are 
concerned  this  was  until  about  the  year  1874 — it  did  not  seem 
to  matter  whether  a  man  possessed  I  Ib.  weight  of  gold  money 
or  15^  Ibs.  weight  of  silver  money — calculated  on  the  quantity 
of  pure  gold  or  silver  in  either — for  he  could  exchange  the 
gold  money  for  an  equivalent  quantity  of  silver  money,  or 
vice  -versa,  at  any  time  he  pleased. 

That  was  the  era  of  legitimate  bimetallism.  As  both 
metals  served  equally  well  (for  coinage)  on  account  of  their 
relatively  high  intrinsic  values,  the  different  states  coined  the 
two  metals  in  the  ratio  by  weight  of  I  to  15-5.  Nevertheless, 
bimetallism  got  into  difficulties.  The  continuous,  although 
small,  fluctuations  in  the  relative  values  of  the  two  metals 
made  it  difficult  to  deal  with  the  necessary  commercial  pay- 
ments in  the  more  advanced  communities.  The  history  of 
bimetallism  in  England  since  the  middle  of  the  sixteenth 
century  shows  this  clearly.  In  1816  England  adopted  a  gold 
standard.  But  when  the  time  came  that  16  or  17  Ibs.,  or  even 
more,  of  silver  could  be  obtained  for  a  single  pound  of  gold,  it 
was  of  course  necessary  that  the  states  should  soon  close  their 
mints  against  the  coinage  of  silver  brought  to  them  by  private 
individuals.  For  if  the  states  continued  legally  bound  to  coin 
the  same  amount  of  money  from  1 5 \  Ibs.  of  silver  as  from  i  Ib. 
of  gold,  it  would  be  possible  to  buy  I5£lbs.  of  uncoined  silver 
for,  let  us  say,  nine-tenths  of  a  pound  of  gold,  and  indeed  for 
a  weight  of  gold  which  constantly  kept  getting  less  ;  if  there- 


248  CHEMISTRY   IN    DAILY   LIFE 

fore  they  had  gone  on  as  before,  all  the  gold  coins  would 
gradually  have  been  driven  out  of  the  countries  in  question. 
For  the  dealers  would  have  sent  these  gold  coins  to  other 
countries  where  they  could  buy  for  I  Ib.  weight  of  them — 
always  calculated  on  the  pure  metal  in  the  coins — not  15J, 
but  perhaps  30,  or  even  more  than  30  Ibs.  of  silver,  which 
silver  they  would  have  brought  back  to  the  states  in  question 
for  coinage.  But  these  states  would  have  been  obliged  to  make 
out  of  15  J  Ibs.  of  silver  a  quantity  of  coins  the  nominal  value 
of  which  should  correspond  with  that  of  i  Ib.  weight  of  gold 
coins,  and  every  one  in  the  countries  in  question  would  have 
been  obliged  to  accept  the  silver  and  gold  coins  as  of  exactly 
equal  value.  In  this  way  the  dealers,  at  the  time  when  the 
ratio  was  I  to  30,  would  have  gained  14^  Ibs.  weight  of  silver 
on  every  pound  weight  of  gold  they  bought  and  then  sold  for 
silver  which  they  proceeded  to  have  coined.  In  more  recent 
times  as  much  as  37  Ibs.  weight  of  silver  could  be  obtained 
for  i  Ib.  of  gold.  Hence  if  the  various  states  had  continued 
to  coin  the  silver  brought  to  their  mints  by  private  people,  a 
man  who  exported  i  Ib.  weight  of  gold  money  and  sold  it  for 
silver  which  he  then  brought  back  and  had  coined  would 
have  gained  as  much  as  21  Ibs.  weight  of  silver.  Under  these 
conditions  it  is  clear  that  not  a  single  gold  coin  would  be  left 
in  the  countries  which  pursued  such  a  policy. 

By  calculating  the  ratio  of  weights  that  have  been 
mentioned  into  gold  we  get  the  following  result.  Until 
the  year  1874,  an  ounce  of  silver  cost  about  60  pence  in 
London,  which  has  always  ruled  the  market  for  the  noble 
metals,  and  the  price  hardly  varied  from  year  to  year ;  but 
at  a  later  time  an  ounce  of  silver  could  be  bought  for  about 
2 1  pence  ;  at  present  it  costs  24  pence. 

As  the  inhabitants  of  the  German  Empire  have  had  a  gold- 
standard  since  1873,  tnev  are  independent  of  fluctuations  in 


BIMETALLISM  249 

the  price  of  silver.  In  countries  which  have  a  gold-standard 
gold  is  the  only  basis  of  currency.  For  that  reason  the  law 
declares  definitely  that  200  marks  are  to  be  coined  from  one 
kilogram  of  silver,  and  that  this  coining  is  to  be  at  the  rate  of 
20  marks  per  head  of  the  population,  without  regard  to  the 
price  of  uncoined  silver.  Therefore  20  marks  in  one-mark 
silver  pieces  are  not  of  nearly  the  same  intrinsic  value  as  one 
2o-mark  gold  piece  ;  for  if  these  twenty  coins  were  melted 
into  a  lump  of  silver,  that  lump,  which  would  of  course 
contain  100  grams  of  uncoined  silver,  would  only  be  saleable 
by  weight,  and  would  fetch  only  a  little  more  than  7  marks, 
as  the  present  selling  price  of  silver  is  about  72  marks  per 
kilogram. 

The  action  of  the  law  has  caused  the  twenty  one-mark 
pieces  to  be  worth  much  more  than  the  silver  in  them 
was  worth  before  coining ;  and  at  the  same  time  the  law 
lays  it  down  that  no  one  is  obliged  to  accept  more  than 
20  marks  in  silver  in  payment  of  a  debt.*  Silver  money 
is  therefore  only  subsidiary  money. 

It  is  certainly  very  remarkable  that  there  should  be 
throughout  Europe  a  party,  known  as  the  bimetallists,  who 
hope  for  the  cure  of  all  agricultural  difficulties,  or  we 
may  say  for  the  better  payment  of  all  labour,  and  an 
increase  in  the  value  of  every  possession,  by  restoring, 
wherever  possible,  the  ratio  between  the  values  of  gold 
and  silver  to  I  to  15^,  and  that  this  party  should  have 
been  very  eager  at  a  recent  time.  The  less  violent  partisans 
of  this  theory  would  be  content,  it  is  true,  with  establishing 
the  ratio  at  I  to  22  for  the  present — for  the  bimetallists 
are  not  unanimously  agreed  as  to  what  they  really  want- 
while,  as  a  matter  of  fact,  the  ratio  keeps  fluctuating  around 
something  like  I  to  37. 
*  Silver  coins  are  legal  tender  up  to  40  shillings  in  this  country.— TR. 


250  CHEMISTRY   IN    DAILY   LIFE 

But  it  is  just  this  fluctuation  which  makes  any  form  of 
bimetallism  impossible  to-day.  For  if  the  various  states 
should  resolve,  by  an  international  agreement,  once  more 
to  coin  gold  and  silver  money  in  g,  fixed  ratio,  say  22  Ibs. 
weight  of  silver  money  for  every  pound  of  gold  money, 
the  effect  of  this  would  be  to  make  silver  more  valuable, 
and  so  to  cause  the  proprietors  of  silver  mines  throughout 
the  world  to  increase  the  production  of  silver — the  increase 
of  which  destroyed  the  old  bimetallism,  for  that  was  in 
no  way  regarded  by  these  silver  owners  while  it  existed — 
and  this  increased  production  would  go  on  until  an  end 
should  happily  be  made  of  the  new  international  bimetallism. 

Nothing  could  be  done  without  an  international  agreement ; 
for  if  a  single  state  were  to  coin  all  the  silver  that  might  be 
brought  to  its  mints  into  money  at  a  ratio  more  favourable 
than  the  ratio  of  i  of  gold  to  37  of  silver,  that  state  would  be 
depleted,  as  we  have  already  said,  of  all  its  gold  coins  in  a  few 
weeks. 

Those  countries,  then,  are  best  off  which  have  a  gold 
currency.  The  inhabitants  of  such  countries  have  a  stable 
standard  of  value,  which  is  not  subject  to  fluctuation,  for  all 
those  things  that  can  be  compared  in  terms  of  gold,  and  for 
this  reason  all  civilised  states  are  in  favour  of  a  gold  standard. 
Until  about  twenty  years  ago  bimetallists  disturbed  people's 
minds  by  asserting  that  there  was  not  nearly  enough  gold  to 
make  it  possible  for  every  country  to  have  a  gold  standard, 
and  that  sufficient  gold  money  could  not  be  coined  to  supply 
the  wants  of  commerce.  But  this  trouble  has  disappeared, 
so  far  as  the  present  generation  is  concerned  at  any  rate, 
since  the  abundant  finds  of  gold  in  South  Africa,  at  Klondyke 
in  North- Western  America,  and  in  West  Australia. 

There  is  one  thing  which  the  bimetallists  would  certainly 
achieve,  as  long  as  they  do  not  get  rid  of  the  fluctuations  in 


BIMETALLISM  251 

the  price  of  silver,  were  they  to  induce  the  civilised  states  to 
inaugurate  an  international  bimetallism  in  that  Utopia  which 
they  depict  to  any  one  who  will  hearken  to  them  as  the 
approaching  economical  rejuvenescence  of  the  nations — for 
none  of  them  has  brought  forward  a  decisive  argument  in 
favour  of  their  assertions  because  no  such  argument  exists, 
for  if  there  were  such  an  argument  it  would  certainly  quickly 
reconvert  the  most  influential  circles  to  bimetallism — and  this 
one  thing  which  they  would  undoubtedly  do  would  be  to 
enable  the  proprietors  of  American  and  Australian  silver 
mines  to  make  yet  much  greater  profits  from  their  mines,  in 
which  profits  Europeans  have  as  yet  no  great  interests. 
Compared  with  these,  the  profits  of  the  European  silver  pro- 
ducers could  not  be  large  because  of  the  smallness  of  the 
European  production. 

All  the  other  advantages  which  the  bimetallists  assert  are 
to  accrue  to  Europe  by  the  adoption  of  their  proposals  rest  on 
unproved  ideas. 

One  cannot  then  be  astonished  that  the  supporters  of 
bimetallism  increased  for  a  time  after  the  subject  began 
to  address  itself  to  the  general  public.  Most  of  the  fre- 
quenters of  the  meetings  of  bimetallists  do  not  grasp  as  a 
whole  the  matters  that  are  put  before  them  because  of  the 
many  difficulties  of  the  subject ;  but  still  they  are  quite  sure 
that  restored  bimetallism— that  mystical  word— will  bring  with 
it  at  least  a  part  of  the  good  fortune  to  which  each  one  thinks 
he  has  an  undoubted  claim,  and  for  that  reason  matters  will 
then  be  different  with  them.  Did  not  some  of  the  troops 
who  were  at  St.  Petersburg  in  1826  at  the  enthronement  of 
the  Tsar  shout  Long  live  the  Constitution  instead  of  Long  live 
Constantine,  because  they  had  been  told  that  the  name  of  the 
new  monarch  was  Constitution  ? 

Independently  of  the  use  of  silver  for  coinage,  there  is  a 


252  CHEMISTRY   IN    DAILY   LIFE 

very  large  demand  for  that  metal.  The  increasing  luxury  of 
the  world  is  constantly  demanding  articles  of  silver  ;  silver 
spoons,  forks,  silvered  knives,  and  so  on  ;  the  demand  for  the 
metal  has  not  ceased  with  the  cessation  of  the  coining  of 
sterling  silver  money  ;  but  the  silver  that  is  produced  in  the 
world  no  longer  finds  its  chief  employment  in  making 
coinage. 


The  base  metals,  to  which  we  now  proceed,  are  extracted 
from  their  ores,  which  are  for  the  most  part  either  oxides  or 
compounds  of  the  metals  with  sulphur.  The  process  of 
extracting  the  metals  from  their  oxides  consists  in  heating 
the  oxides  mixed  with  coal  or  charcoal  in  suitable  furnaces, 
whereby  the  oxide  is  said  to  be  reduced  to  metal. 

Oxide  of  iron  4-  carbon  =  iron  +  carbon  monoxide. 

To  convert  the  sulphur  compounds  into  oxides,  and  so  to 
obtain  compounds  from  which  the  metals  can  be  extracted  on 
the  large  scale,  it  is  necessary  to  roast  the  sulphides  in  the 
air  ;  in  this  process  the  sulphur  is  burnt  to  sulphurous  acid, 
and  the  metal  to  oxide,  which  is  then  reduced  by  heating 
with  carbon.  For  example  : 

Sulphide  of  zinc  4-  oxygen  (from  the  air)  =  sulphurous  acid  +  oxide  of  zinc 

Zincblcnde. 

and 

Zinc  oxide  +  carbon  =  zinc  +  carbon  monoxide. 

Were  the  sulphurous  acid  to  escape  into  the  air  it  would 
destroy  all  the  plant  life  in  the  neighbourhood ;  it  is 
therefore  generally  collected,  nowadays,  by  the  help  of 
improved  arrangements  in  the  furnaces,  and  converted  into 


EXTRACTION    OF    IRON  253 

sulphuric  acid.  The  equation  just  given  represents  the 
carbon  as  being  burnt  only  to  carbon  monoxide  when  a 
metallic  oxide  is  reduced  to  metal  by  heating  with  carbon, 
whereas  in  other  cases  we  saw  that  it  was  burnt  to  carbonic 
acid.  The  reason  for  this  is  that  the  temperature  required 
for  the  reduction  of  the  metallic  oxides  is  so  high  that  at 
that  temperature  the  carbon  is  able  to  bind  to  itself  only  a 
single  atom  of  oxygen  ;  the  carbon  monoxide  that  is  formed 
in  this  way  can  at  another  time  combine  with  a  second  atom 
of  oxygen  and  thus  be  burnt  to  carbonic  acid. 

The  following  equations  clearly  present  the  changes : 

Carbon  +  one  atom  of  oxygen  =  carbon  monoxide, 
c       +  O  CO 

Carbon  monoxide  -f  one  atom  of  oxygen  =  carbonic  acid. 

CO  +  O  COa 

Carbon  monoxide  is  the  intermediate  stage  of  the  burning 
of  carbon  to  carbonic  acid.  We  have  gone  into  this  matter 
with  some  fulness  because  we  shall  have  to  make  use  here- 
after of  this  more  accurate  statement  of  what  occurs  in  these 
processes. 

We  shall  now  make  a  more  special  study  of  the  extraction 
of  iron.  Three  sorts  of  iron  have  been  distinguished  for  very 
many  years. 

Pig  or  cast  iron,  containing  2-3  per  cent,  or  more  than  2-3  per  cent,  of 
carbon  ; 

Steel,  which  contains  r6  per  cent.,  or  less  than  this,  of  carbon,  but 
more  carbon  than  the  third  variety  ; 

Wrought  iron,  containing  about  half  a  per  cent,  of  carbon. 

Pig  iron  is  relatively  easily  fusible,  and  can  be  cast,  but 
not  forged  ;  steel  can  be  worked  in  the  forge,  and  the  articles 
made  in  this  way  can  then  be  tempered  ;  wrought  iron  can 
also  be  forged,  but  not  tempered  afterwards.  By  forging  is 


254  CHEMISTRY  IN   DAILY  LIFE 

meant  the  softening  at  a  full  red  heat  to  such  an  extent  that 
the  iron  can  be  worked  by  the  hammer  into  any  desired 
form.  Both  steel  and  wrought  iron  can  be  welded,  that  is, 
two  pieces  can  be  joined  homogeneously  by  hammering  at  a 
white  heat. 

Many  other  kinds  of  iron  are  distinguished  in  the  iron 
manufacture  of  to-day,  but  we  shall  discover  that  the  pre- 
ceding classification  is  sufficient  for  our  purposes. 

All  commercial  iron,  then,  contains  carbon.  While  it  is  well 
known  that  endeavours  are  made  to  obtain  all  other  metals 
as  free  from  impurities  as  possible,  because  their  peculiar 
properties  are  then  most  distinctly  apparent,  the  case  is 
different  with  iron.  The  contamination  of  iron  with  carbon, 
if  such  an  expression  may  be  used  in  this  connection,  is 
required  in  order  to  give  to  the  iron  those  diverse  properties 
which  make  it  the  most  serviceable  of  all  the  metals. 

Iron  takes  up  more  than  2-3  per  cent,  of  carbon  only  at  a 
very  high  temperature  ;  hence  pig  or  cast  iron  was  quite 
unknown  to  the  ancients.  Wrought  iron,  however,  has  been 
known  for  ages.  It  is  supposed  to  have  been  first  made 
about  1500  B.C.  by  the  Philistines.  The  production  of  this 
iron,  however,  depended  on  the  degree  of  civilisation  of -a 
people,  for  it  is  told  by  Caesar  that  when  he  came  to  Britain 
about  50  B.C.  gold  and  iron  were  nearly  equally  valuable 
there,  as  the  inhabitants  possessed  only  those  small  quantities 
of  the  two  metals  which  were  brought  to  the  country  by 
traders.  Methods  of  extracting  iron  were  unknown  at  that 
time  in  England,  which  is  the  country  where  the  most 
important  discoveries  in  that  direction  were  made  at  later 
times,  and  is  also  the  country  whose  output  of  iron  was  for 
centuries  greater  than  that  of  any  other,  although  the  output 
of  England  has  been  exceeded  within  recent  years,  not  only 
by  that  of  the  United  States  of  America,  a  country  with  an 


EXTRACTION   OF   IRON  255 

area  enormously  greater  than  the  area  of  England,  but  also 
by  that  of  Germany.* 

Enormous  deposits  of  iron  ore  were  discovered  in  America 
in  1890.  In  1892,  4,245  tonnes  (1,000  kilograms  =  I  tonne) 
of  ore,  containing  58  per  cent,  of  iron,  were  raised  ;  in  1894, 
17,921,705  tonnes;  and  in  1907,28,000,000 tonnes  were  raised. 

The  extraction  of  iron  cannot  be  made  clear  except  we 
first  realise  the  method  and  manner  of  the  production  of  the 
high  temperatures  that  are  required  in  the  processes  ;  we 
must  therefore  approach  the  subject  of  the  manufacture  of 
iron  from  this  side. 

If  wood  or  coal,  or  other  combustible  material,  burns  on 
the  ground,  only  a  flickering  fire  of  little  use  as  a  source  of 
heat  is  obtained,  for  the  supply  of  air,  which  is  needed  for 
burning  the  carbon,  is  very  limited.  But  matters  are  soon 
altered  if  the  heating  material  is  burnt  on  a  support  that  is 
perforated  so  that  the  air  can  enter  from  beneath.  We  do 

*  About  a  hundred  years  ago,  in  1807,  the  world's  annual  output  of 
iron  was  760,000  tonnes  ;  it  is  now  about  61,000,000  tonnes  ;  this  means 
that  about  120,000  kilos,  of  crude  iron  are  produced,  and  used,  every 
minute  of  the  year.  The  following  figures  give  the  output  of  pig-iron 
for  each  of  the  chief  iron-producing  countries,  in  the  years  1882  and  1909  : 

1882  1909 

United  States  of  America     .         .         .     4,600,000  27,636,687 

Germany 3,400,000  i4>793»325 

Great  Britain 8,600,000  10,380,212 

France 2,000,000  4,032,459 

Russia 400,000  2,740,000 

Austria- Hungary 600,000  2,010,000 

Belgium 700,000  1,803,500 

Canada 752,053 

Sweden 400,000  604,300 

Spain 100,000  367>ooo 

Italy 215,000 

All  other  countries        ....        500,000  525,000 

21,300,000  65,859,536 
(A  tonne  =  1000  kilos.  =  '9842  ton.) 


256  CHEMISTRY  IN    DAILY  LIFE 

this  when  we  burn  a  fire  in  a  grate  ;  and  if  we  also  insure 
the  speedy  removal  of  the  carbonic  acid  and  the  other 
products  of  combustion,  by  fixing  an  exit  pipe  at  a  proper 
distance  above  the  fire,  then  the  regular  stream  of  air  which 
flows  into  the  fire  brings  about  a  uniformly  rapid  combustion 
of  the  materials  in  the  grate.  A  pipe  of  this  kind,  which 
takes  the  form  of  a  chimney  in  a  dwelling  house,  acts  as  a 
means  of  producing  a  draught,  for  the  carbonic  acid  formed 
in  the  burning  and  the  nitrogen  that  comes  in  with  the  air, 
being  much  heated  by  the  fire,  become  lighter,  bulk  for  bulk, 
than  the  surrounding  air,  and  therefore  tend  to  ascend,  and 
hence  to  cause  a  current  inwards  of  fresh  air  to  supply  their 
place. 

Many  metallic  oxides  may  be  reduced  in  a  fire  of  the  kind 
described  with  the  help  of  carbon,  but  oxide  of  iron  cannot 
be  reduced.  This  oxide  is  reduced  only  when  the  fire  is 
saved  the  trouble  of  sucking  in  the  air  by  blowing  the 
air  supply  into  the  fire,  whereby  a  very  rapid  combustion 
is  of  course  produced.  Every  smithy  fire  is  an  arrangement 
of  this  kind  wherein  air  is  blown  into  the  fire  by  the  smith's 
bellows. 

The  ancients  reduced  oxide  of  iron  in  a  smithy  fire  (see 
fig.  19).  They  sometimes  obtained  wrought  iron  and  some- 
times steel,  for,  according  to  the  manner  of  working,  sometimes 
less  and  sometimes  more  carbon  entered  into  the  iron,  and  it 
is  upon  the  quantity  of  this  constituent  that  the  production 
of  one  or  the  other  of  these  varieties  of  iron  depends.  The 
results  were  better  or  worse  according  to  the  purity  of  the 
iron  ore  used  and  the  skill  of  the  workmen  who  handed 
down  the  art  from  one  generation  to  another.  Hence  came 
the  great  reputation  of  the  blades  of  Damascus  and  Toledo, 
for  instance  ;  for  the  production  of  steel,  which  is  a  very 


EXTRACTION   OF   IRON 

difficult  art  when  only  a  smith's  forge  is  available,  had 
become  a  specialty  of  these  districts  and  had  been  brought 
to  great  perfection. 

Only    those    iron    ores   which    are    comparatively    easily 


reduced  can  be  worked  in  a  smith's  forge.  But  the  production 
of  iron  spread  gradually  to  different  countries,  and  as  easily 
reduced  ores  were  not  to  be  had  everywhere,  it  became 
necessary  to  find  means  for  increasing  the  heat  of  the 
furnace.  This  was  done  by  building  stones  around  the 
smithy  fire  and  so  converting  it  into  a  blast  furnace.  The 
17 


258  CHEMISTRY  IN  DAILY  LIFE 

heat  of  the  fire  was  not  then  lost  in  warming  the  surrounding 
air,  but  the  stones  became  red  hot  and  so  concentrated  the 
heat  more  in  one  place,  and  the  temperature  was  raised  so 
much  that  the  reduced  iron  took  up  four,  or  more  than  four 
per  cent,  of  carbon,  and  the  pig  iron  thus  produced  ran  from 
the  furnace  in  a  liquid  state.  This  discovery  seems  to  have 
been  made  in  the  southern  part  of  Alsace  near  where  the 
town  of  Mulhouse  now  stands ;  at  any  rate  the  oldest 
specimens  of  pig  iron  that  are  known  came  from  that 
neighbourhood  about  the  year  1490.  The  invention  of  pig 
iron  was  made  about  the  time  that  saw  the  discovery  of 
America. 

The  manufacture  of  pig  iron  spread  somewhat  slowly, 
and  it  was  not  till  1547  that  it  began  to  be  practised  in 
England.  The  first  iron  smelting  in  Prussia,  the  territorial 
extent  of  which  was  very  different  at  that  time  from  what  it 
is  now,  took  place  in  1667. 

The  blast  furnaces  that  are  in  use  to-day  are  enormously 
larger  than  those  of  these  early  days  (see  fig.  20).  With 
regard  to  the  production  of  iron  in  these  furnaces,  the  follow- 
ing points  should  be  particularly  noticed.  The  iron  oxide  is 
reduced  to  iron  by  the  carbon  (coal)  in  the  furnace,  and  the 
iron  sinks  gradually  downwards  until  it  comes  to  a  part  of 
the  furnace  which  is  so  hot  that  the  iron  takes  up  a  quantity 
of  carbon  sufficient  to  cause  it  to  melt ;  but  after  that,  the 
molten  iron  has  to  pass  the  zone  whereat  the  air  is  blown 
into  the  furnace,  and  at  this  place  it  would  be  again  burnt  to 
oxide  of  iron  were  not  an  especial  precaution  taken  to 
prevent  this.  The  formation  of  slag  is  the  precautionary 
measure  that  is  adopted. 

Slag  is  a  kind  of  glass ;  it  consists  of  double  silicates  (see 
p.  200).  Besides  oxide  of  iron  and  coal,  lime-stone  and  clay 
(the  latter  is  a  silicate  of  alumina),  and  when  necessary  sand 


BLAST  FURNACES 


259 


also,  are  thrown  into  the  blast  furnace.  These  things  vary  in 
different  neighbourhoods  and  also  in  accordance  with  the 
constituents  of  the  ores  that  are  to  be  smelted,  the  most 
easily  accessible  and  the  cheapest  substances  that  are  suitable 
for  the  purpose  being  chosen.  Those  that  have  been 
mentioned  are  the  most  commonly  used  ;  at  the  temperature 


Fig.  20.— Blast  furnace  of  1830. 

of  the  furnace  they  react  to  form  a  double  silicate  of  lime  and 
alumina,  which  is  a  kind  of  glass. 

The  mixture  of  the  substances  that  are  to  produce  the  slag 
is  always  selected  so  that  they  run  together  to  a  glass  only 
after  the  iron  has  taken  up  enough  carbon  to  convert  it  into 
pig  iron ;  this  glass  then  covers  the  individual  molten 
particles  of  iron  and  protects  these  from  the  effects  of  the  air 


26O  CHEMISTRY  IN   DAILY  LIFE 

blast.  And  in  this  way  the  iron  passes  the  zone  where  the 
blast  is  sent  in  without  being  reburnt  to  oxide.  Lower  down 
in  the  furnace  the  heavy  liquid  iron  separates  from  the  lighter 
melted  glass,  and  both  flow  out  of  the  furnace  as  liquids.* 
When  the  iron  solidifies  it  is  called  pig  iron,  and  the  solidified 
glass  is  called  slag.  (Slag  is  used  for  making  cement, 
see  p.  211.)  It  was  only  after  the  discovery  of  pig  iron 
that  iron  making  became  a  great  industry  in  the  modern 
meaning  of  that  term — that  is,  one  of  those  industries  that 
never  dream  of  a  night's  rest.  Up  till  that  time  the  smith 
could  get  ready  each  day  two  or  perhaps  three  blocks  of 
iron,  each  weighing  about  80  Ibs.,  and  these  he  might  or 
might  not  work  up  the  following  day.  But  the  preparation 
of  pig  iron  is  carried  on  in  quite  a  different  way.  When 
a  blast  furnace  is  started  it  must  be  kept  going  day  and 

*  The  representation  of  the  blast  furnace  in  fig.  20  is  diagrammatic, 
because  such  a  representation  elucidates  the  preparation  of  pig  iron 
better  than  an  exact  drawing  of  one  of  the  monstrous  modern  furnaces 
would  do.  A  modern  furnace  requires  six  or  seven  pipes  for  blowing  in 
air  [called  tuyeres],  whereas  only  one  is  represented  in  the  figure. 
Moreover,  the  furnace  is  shown  open  at  the  top  whereat  the  flames  are 
escaping  ;  but  this  is  not  the  case  in  actual  furnaces  nowadays.  The  air 
which  is  blown  into  the  furnace  is  heated  to  a  very  high  temperature 
before  its  admission  into  the  furnace.  The  carbon  of  the  coal  is  burnt  to 
carbonic  acid.  But  this  extremely  hot  gas  reacts  with  the  higher  layers 
of  hot  coal  to  form  carbon  monoxide.  Thus 

CO.,  +  C  =  2CO. 

Carbonic  acid  +  carbon  =  carbon  monoxide. 

Hence  carbon  monoxide,  which  is  an  inflammable  gas,  escapes  from  the 
furnace,  mixed  with  much  nitrogen.  In  olden  times  this  mixture,  which 
contained  from  24  to  34  per  cent,  of  combustible  gas,  was  allowed  to  burn 
at  the  mouth  of  the  furnace,  and  so  to  be  lost  (as  is  shown  in  the  figure)  ; 
nowadays  the  furnace  is  closed  by  a  hood,  and  the  carbon  monoxide  is 
led  from  under  this  hood  to  places  where  it  is  burnt,  and  the  heat  is  used 
for  evaporating,  or  for  heating  the  air  to  be  sent  into  the  furnace,  or  for 
other  purposes  of  a  similar  kind.  The  gas  from  the  blast  furnaces  is 
also  used  for  driving  gas  engines. 


PIG  IRON  26l 

night,  else  it  would  not  get  hot  enough  to  melt  any 
iron  at  all  ;  but  in  return  for  this  the  furnace  produces 
large  quantities  of  pig  iron,  which  has  thus  become  a  cheap 
commodity. 

Pig  or  cast  iron  then  contains  more  than  23  per  cent, 
of  carbon,  and  if  it  were  possible  to  burn  away  a  part  of 
this  carbon  either  steel  or  wrought  iron  (see  page  253) 
would  be  produced.  And  such  a  burning  away  of  carbon 
is  actually  accomplished.  When  pig  iron  is  heated  in  a 
forge  fire  with  free  access  of  air  a  part  of  the  carbon  in 
the  iron  is  burnt  away,  the  mass  becomes  pasty  and  does 
not  run  to  a  liquid,  and  either  steel  or  wrought  iron  is 
formed  according  to  the  skill  of  the  workman.  It  is  much 
easier  and  cheaper  to  make  wrought  iron  than  steel  in  this 
way,  because  it  is  very  difficult  to  hit  the  point  whereat 
just  enough  carbon  is  left  in  the  iron  to  give  it  the  pro- 
perties of  steel.  But  in  making  wrought  iron  it  is  only 
necessary  to  burn  away  as  much  of  the  carbon  as  possible, 
for  enough  always  remains  to  give  the  whole  of  what  is 
left  the  qualities  of  wrought  iron.  Now  it  was  found  to 
be  so  much  easier  to  make  wrought  iron  from  pig  iron 
than  to  manufacture  it  directly  from  the  ores  by  the  older 
process,  which  was  the  only  method  available  before  the 
discovery  of  pig  iron,  that  the  ancient  method  was  soon 
abandoned,  and  as  a  consequence  the  manufacture  of  pig 
iron  in  the  blast  furnace  has  become  the  foundation  of  the 
whole  iron  industry. 

This  condition  of  affairs  had  been  attained  as  early  as 
1620.  The  manufacture  of  pig  iron  had  become  a  large 
concern  in  England  by  that  time,  as  the  conditions  were 
more  favourable  in  that  country  than  elsewhere.  The 
intelligence  of  the  inhabitants  eagerly  turned  to  the  best 
account  the  large  quantities  of  iron  ores  that  were  raised 


262  CHEMISTRY  IN   DAILY   LIFE 

in  that  country,  and  the  many  rivers  made  it  possible  to 
transport  the  prepared  iron  without  difficulty  to  other  lands. 
The  roads  at  that  time,  being  badly  constructed  and  easily 
disturbed  by  rains,  were  not  adapted  for  the  transport  of 
great  quantities  of  iron  ;  hence  the  manufacture  of  iron 
could  not  be  carried  on  profitably  at  any  great  distance  from 
rivers  or  from  the  sea. 

Wood  charcoal  was  employed  as  fuel  in  the  blast  furnaces ; 
but  the  great  demand  for  wood  led  to  the  visible  disappear- 
ance of  the  forests — independently  of  the  destruction  of 
forests,  which  was  but  little  heeded  in  those  days — and  to 
the  imperative  necessity  of  finding  some  substitute  for  wood. 
Coal  at  once  suggested  itself.  But  a  blast  furnace  cannot 
be  worked  with  coal  as  the  fuel  ;  for  before  it  burns,  coal 
becomes  pasty  and  tarry  matter  distils  from  it,  and  if  coal 
were  used  in  the  blast  furnace  the  single  pieces  would  get 
glued  together  so  that  the  air  blast  could  not  penetrate  the 
mass,  and  the  working  of  the  furnace  would  be  stopped.* 
The  suggestion  was  made  to  change  coal  into  coke — that  is, 
to  heat  the  coal  in  a  closed  vessel  where  it  cannot  burn  for 
lack  of  air.  All  the  volatile  and  fusible  matters  in  the  coal 
are  driven  out  by  this  treatment,  and  a  hard  mass  remains, 
which  can  be  used  as  fuel  in  the  blast  furnace  because  it 
will  burn  without  caking  together.  In  making  coke  for  use 
in  the  blast  furnace  no  attention  is  paid  to  the  volatile 
matter  of  the  coal ;  it  is  only  the  residue— the  coke— that 
is  important  (cf.  pp.  28  to  30). 

Coke  began  to  be  used  in  blast  furnaces,  in  England,  about 
the  year  1700 ;  and  as  it  then  became  possible  to  obtain  any 
desired  quantity  of  fuel  the  production  of  cast  iron  went  on 

*  Nevertheless,  bituminous  coal  is  used  in  blast  furnaces  in  Scotland 
and  North  Staffordshire,  and  in  parts  of  the  United  States.— TR. 


BLAST  FURNACES  263 

increasing  very  considerably  until  about  the  beginning  of  last 
century,  when  that  enormous  advance  began,  the  end  of 
which  we  cannot  yet  see. 

Coke  is  so  hard  that  a  blast  furnace  may  be  built  about 
30  metres  [92  feet]  high  without  the  contents  getting 
crushed  and  crumbled.  In  the  olden  days  it  would  not 
have  been  possible  to  get  the  enormous  quantities  of  raw 
material  which  such  a  furnace  requires  into  the  furnace ; 
and  it  was  only  after  the  invention  of  steam  engines  and 
railways  that  it  became  possible  to  feed  furnaces  of  such 
a  size. 

A  blast  furnace  using  charcoal  as  fuel,  such  as  may  be 
found  at  work  to-day  in  Styria,  could  turn  out  daily,  about 
the  year  1800,  from  3,000  to  4,000  kilograms  [nearly  three  to 
four  tons]  of  cast  iron ;  but  a  very  large  modern  blast  furnace, 
using  coke,  produces  daily  nearly  600,000  kilograms  [about 
590  tons]  of  the  same  substance. 

The  modern  blast  furnace  is  not  built  of  stone,  but  almost 
wholly  of  plates  of  wrought  iron,  or  steel,  which  are  covered 
on  the  inside  with  a  layer,  some  4  inches  thick,  of  fire- 
resisting  stone.  The  iron  plates  must  be  continually  cooled  ; 
about  6  litres  of  cold  water  are  required  per  minute  to  cool  each 
square  metre  of  surface  [about  one  gallon  of  water  per  minute 
for  each  square  yard  of  surface].  In  1880,  about  8  tonnes  of 
coke  were  used  for  each  tonne  of  pig  iron  produced  ;  in  1850, 
only  about  3  tonnes  of  coke  were  used  ;  and  in  1900,  about 
i  tonne  of  coke  was  required,  which  is  about  the  minimum 
quantity  theoretically  possible.  The  immense  importance  of 
iron  in  the  scientific  life  of  peoples  is  made  clear  by  the  fact 
that  the  money  value  of  the  iron  produced  in  the  year  1900, 
although  iron  is  the  cheapest  of  all  metals,  was  one  and  a  half 
times  greater  than  the  value  of  all  the  other  metals  taken 
together, "including  gold  and  silver. 


264  CHEMISTRY  IN   DAILY  LIFE 

While  the  mechanical  parts  of  the  operation  of  iron 
smelting  were  being  brought  to  perfection,  chemistry  was 
busily  engaged  in  trying  to  elucidate  the  processes  that 
occur  in  the  blast  furnace,  for  these  processes  are  certainly 
not  so  simple  as  we  have  represented  them  in  the  sketch 
that  has  been  given.  And  since  it  has  become  perfectly 
clear  that  the  properties  of  different  kinds  of  iron  are 
conditioned  by  the  percentage  quantity  of  carbon  which 
each  contains — a  statement  that  is  far  from  being  self- 
evident — advance  has  ceased  to  be  slow  ;  and  indeed  such 
rapid  progress  has  been  made  on  the  basis  of  this  knowledge 
that  the  present  generation  may  be  said  to  be  passing  from 
the  age  of  iron  to  the  age  of  steel. 

The  remark  has  already  been  made  that  scarcity  of 
charcoal  led  in  England  to  the  erection  of  blast  furnaces 
which  should  use  coke  as  their  fuel.  All  the  pig  iron 
obtained  by  the  use  of  these  furnaces,  except  what  is 
employed  for  making  articles  of  cast  iron,  was,  and  is, 
manufactured  into  steel  or  into  wrought  iron.  The  pre- 
paration of  wrought  iron  was  carried  on  in  small  furnaces 
with  strong  air  draughts,  wherein  the  carbon  was  gradually 
burnt  away  until  only  about  J  per  cent,  remained  ;  the 
product  was  wrought  iron.  It  was  necessary  to  use  charcoal 
for  this  purpose,  because  the  ashes  of  coal  or  coke  contain 
substances  which  react  chemically  with  the  iron  while  it  is 
being  worked  up  with  the  fuel  in  such  a  way  that  the 
wrought  iron  produced  is  quite  useless. 

While  it  was  possible  many  years  ago  to  obtain  pig 
iron,  produced  in  large  works,  in  quantity  and  at  a  low 
price,  wrought  iron  long  remained  as  expensive  as  it  had 
ever  been,  for  it  was  still  made  on  a  small  scale,  and  each 
lump  of  iron  was  worked  on  the  hearth  of  a  furnace,  just 
as  used  to  be  done  in  olden  days ;  and  in  addition  to 


PREPARATION   OF  WROUGHT  IRON 


265 


this,   charcoal,   which    is    an    expensive   fuel,   was    used    in 
making  it. 

But  a  revolution  was  brought  about  by  the  discovery 
made  by  Cort,  an  Englishman,  and  patented  by  him  in  the 
year  1784.  Cort  hit  on  the  plan  of  separating  the  fire  from 
the  pig  iron  in  making  wrought  iron  ;  as  the  ashes  of  the 
combustible  material  were  thus  prevented  from  coming  into 
contact  with  the  iron  these  ashes  had  no  influence  on  the 
product  He  carried  on  the  making  of  wrought  iron  in  a 
reverberatory  furnace ;  and  his  process,  which  is  called 


Fig.  21.— A,  Grate,  whereon  the  fuel  is  burnt.     B,  Fire  bridge.     C,  Furnace 
bed,  whereon  the  iron  is  heated.    D,  Flue  bridge.    E,  Flue.    F,  Chimney. 

"  puddling,"  has  remained  in  use  until  now,  although  changes, 
to  which  we  shall  refer  immediately,  have  been  made  in  the 
arrangement  of  the  furnace.  In  a  reverberatory  furnace  it  is 
only  the  flame  of  the  burning  fuel  that  plays  on  the  iron  (see 
fig.  21).  The  iron  does  not  come  into  contact  with  the  ashes 
of  the  fuel. 

This  process  is  capable  of  manufacturing  large  quantities 
of  wrought  iron,  inasmuch  as  a  great  many  pigs  of  iron  may 
be  placed  at  the  same  time  on  the  bed  of  the  furnace,  which 
is  separated  from  the  fuel  by  the  fire  bridge,  and  the  carbon 
of  these  pigs  will  be  gradually  burnt  away  until  only  a  very 


266 


CHEMISTRY  IN   DAILY  LIFE 


little   is   left ;    and  as  the  furnaces   must   be  kept  working 

uninterruptedly  day  and  night, 
that  the  proper  temperature  may 
be  maintained,  the  manufacture 
of  wrought  iron  has  become  one 
of  those  industries  that  are  con- 
ducted on  a  very  large  scale. 

Previous  to  the  improvement 
made  by  Cort  it  had  been 
customary  to  hammer  out  each 
lump  of  iron,  as  it  was  made  in 
the  forge,  by  hand,  or  by  the  use 
of  a  somewhat  larger  hammer 
worked  by  a  water-wheel.  The 
surfaces  of  the  articles  of  wrought 
iron  made  by  this  older  process 
were  never  quite  smooth,  and  the 
marks  of  the  blows  of  the  hammer 
could  be  seen  upon  them,  even 
on  iron  bands,  which  to-day  are 
made  as  smooth  as  if  they  had 
been  polished. 

The    masses   of  wrought   iron 
produced  by  the   older   methods 
of    puddling     were     not    at    all 
amenable    to    further    treatment. 
Cort    introduced    the    rolling    of 
wrought    iron.      He    shaped   the 
pieces  of  iron  that  left  the  furnace 
into  the  desired  forms  by  squeez- 
ing them  while  red  hot  between  rollers  (see  fig.  22).     If  the 
two  rollers  work  close   on  one  another,  and  corresponding 


ROLLING  WROUGHT  IRON  267 

pieces  are  cut  out  of  the  upper  and  under  rollers,  band  or 
square  iron  is  obtained,  and  if  the  indentations  are  truly  cut 
the  bands  must  come  out  of  the  rolling  mill  with  perfectly 
smooth  surfaces.  If  a  cutting  the  shape  of  the  top  of  a 
railway  rail  is  made  in  the  upper  roller,  and  one  which 
has  the  form  of  the  lower  part  of  such  a  rail  is  made 
in  the  under  roller,  then  the  rolling  mill  turns  out  rails.  A 
sheet  of  iron  is  obtained  by  passing  a  piece  of  iron  between 
two  smooth  rollers  fixed  at  a  convenient  distance  from  one 
another  ;  and  so  on. 

Like  many  other  great  inventors,  Cort  derived  no  material 
advantages  from  his  ideas  and  labours  which  have  done  so 
much  to  advance  civilisation.  The  many  researches  that 
were  needed  to  bring  his  ideas  into  practicable  shape 
swallowed  up  his  means,  and  he  died  in  poverty. 

James  Watt  had  invented  the  steam  engine  towards  the 
end  of  the  eighteenth  century.  But  the  work  which  the 
engine  could  do  was  very  limited,  because  the  steam  that 
was  needed  to  keep  it  going  could  be  produced  only  in  cast- 
iron  boilers,  and  no  one  at  that  time  knew  how  to  make 
these  of  considerable  size.  This  was  not  changed  until 
the  process  of  rolling  iron  made  it  possible  to  manufacture 
large  uniform  plates  of  wrought  iron.  Large  boilers  can 
evidently  be  made  by  riveting  such  plates  together,*  and 
such  quantities  of  steam  can  be  produced  in  these  boilers  as 
suffice  to  set  in  motion  the  largest  machines. 

Attempts  began  to  be  made  in  the  early  years  of  last 
century  to  employ  steam  engines  in  place  of  horses  for 
traction  purposes. 

As  has  been   mentioned,  most  of  the  English  mines  are 
situated  near  rivers,  and  it  was  long  ago  customary  to  lay 
down  wooden   tracks   for   the   easier   conveyance   of  heavy 
*  Steel  plates  are  used  nowadays. 


268  CHEMISTRY   IN   DAILY  LIFE 

loads  from  the  mines  to  the  rivers ;  sleepers  were  placed  on 
the  ground,  and  then  joined  into  a  continuous  track  by  long 
pieces  of  wood.  In  order  to  do  away  with  the  need  of 
frequently  renewing  the  long  pieces  of  wood  between  which 
the  horses  walked  the  custom  was  to  lay  boards  over  these, 
so  that  when  the  boards  were  worn  out  by  the  passage  of 
the  wheels  over  them  they  could  be  replaced  by  others. 

In  the  year  1767  the  iron  industry  was  affected  by  an 
extraordinary  crisis,  which  became  so  severe  that  at  last 
cast  iron  was  quite  unsaleable.  A  large  ironworks  that  had 
a  considerable  stock  of  pig  iron  cast  a  part  of  its  stock  into 
oblong  plates,  that  the  iron  might  not  be  lying  altogether 
useless,  and  laid  these  down  on  the  foundations  of  a  wooden 
tramway  in  place  of  the  boards  that  had  been  used  before ; 
this  road  thus  became  the  first  railway,  as  we  call  such  a 
construction  nowadays. 

The  experiment  turned  out  a  great  success.  The  horses 
were  able  to  draw  much  heavier  loads  on  this  smooth  support 
than  on  the  boards  that  were  formerly  used,  and  the  wear 
and  tear  of  the  iron  was  extremely  small.  When  the  crisis 
in  the  iron  trade  was  over,  not  only  did  this  railway  remain, 
but  all  the  other  works  gradually  adopted  the  new  con- 
trivance. 

Here,  then,  in  the  literal  meaning  of  the  word,  was  laid 
the  foundation  for  steam  carriages.  Stephenson  had  about 
that  time  constructed  the  first  locomotive  that  was  of 
practical  use  for  the  conveyance  of  human  beings. 

An  examination  of  the  English  patent  literature  of  that 
period  shows  what  a  vast  number  of  proposals  was  made,  and 
how  many  investigations  were  undertaken,  with  regard  to 
steam  carriages,  all  of  which  came  to  nothing ;  and  it  also 
makes  one  better  appreciate  the  esteem  in  which  his  con- 
temporaries held  the  discoverer  who  at  last  hit  upon  the  true 


CEMENTATION   STEEL  269 

solution  of  an  extremely  difficult  problem  which  had  been 
attacked  by  so  many  others. 

After  the  invention  of  the  process  of  puddling  it  was  easy 
to  obtain  both  cast  and  wrought  iron  ;  but  circumstances  still 
remained  very  unfavourable  to  the  production  of  steel, 
which  is  the  most  valuable  form  of  iron  so  far  as  usefulness 
is  concerned. 

It  is  just  as  difficult  to  make  steel  from  pig  iron  by 
puddling  as  it  used  to  be  to  make  wrought  iron  by  the  old 
forge  method.  There  is  no  theoretical  objection  to  the 
method,  for  all  that  need  be  done  is  to  stop  the  puddling 
when  the  iron  contains  just  enough  carbon  to  form  steel  ; 
nevertheless  this  can  scarcely  be  done  in  practice. 

As  long  ago  as  the  beginning  of  the  eighteenth  century, 
that  is,  long  before  the  invention  of  puddling,  a  new  method 
of  preparing  steel  was  found  out  in  Northern  France;  the 
steel  made  by  that  method  was  known  as  cementation  steel. 
The  earliest  truly  scientific  work  on  this  subject  was  carried 
out  by  Reaumur,  who  lived  at  that  time,  and  whose  name  is 
generally  known  in  connection  with  the  thermometric  scale 
which  he  introduced. 

If  sufficient  carbon  could  be  added  to  wrought  iron  to 
bring  up  the  quantity  of  carbon  from  \  to  about  I  \  per  cent., 
then,  in  accordance  with  the  sketch  given  on  p.  253  of  the 
different  kinds  of  iron,  we  should  expect  that  steel  would  be 
produced.  The  preparation  of  cementation  steel  depends  on 
this  principle.  The  wrought  iron  is  cut  into  bars,  and  these 
are  packed  in  charcoal  powder  in  fireclay  chests  capable  of 
containing  about  8,000  kilos  (say  8  tons),  set  in  a  convenient 
manner  in  a  furnace  which  is  kept  heated  to  about  1,000°  C. 
(about  i,8oo°F.)  for  a  period  of  six  to  eight  days.  Under 
these  conditions  a  gradual  permeation  of  the  iron  by  the 


270  CHEMISTRY  IN   DAILY  LIFE 

carbon  takes  place,  and  the  iron  is  changed  completely  into 
steel. 

Steel  made  in  this  way  cannot  be  quite  homogeneous,  for 
the  outer  parts  of  the  bars  will  be  richer  in  carbon  than  the 
inner  portions.  A  remedy  for  this  was  sought  in  the  vigorous 
working  of  the  steel  under  the  hammer. 

In  1730  an  English  watchmaker  called  Huntsman  dis- 
covered a  perfectly  homogeneous  steel  that  cannot  be  surpassed 
to-day.  He  found,  as  every  one  else  did,  that  very  many  of 
the  watch  springs  he  worked  with  snapped,  because  of  the 
unequal  character  of  the  steel  of  which  they  were  made,  and 
in  attempting  to  remedy  this  he  discovered  that  small 
quantities  of  cementation  steel  could  be  melted  in  crucibles 
placed  in  an  extremely  hot  furnace. 

This  can  be  easily  understood  by  us  ;  we  know  that  iron 
containing  2*3  per  cent,  of  carbon  rnelts  comparatively 
readily,  and  there  seems  to  be  no  reason  why  iron  containing 
less  carbon  should  not  also  melt  if  a  sufficiently  high 
temperature  were  attained. 

The  cast  steel  discovered  by  Huntsman  is  perfectly 
homogeneous  throughout,  and,  as  the  hardness  of  steel  is 
not  diminished  by  melting,  this  cast  steel  is  a  material  that 
cannot  be  replaced  for  many  purposes  by  anything  else. 
The  method  of  manufacture  remained  a  secret  with  certain 
English  makers,  who  asked  fancy  prices  for  their  steel ;  and 
these  prices  were  paid  because  a  material  equally  suitable 
for  many  purposes  could  not  be  obtained  anywhere  else. 
Many  efforts  were  of  course  made  to  find  out  the  method 
whereby  this  English  steel  was  secretly  manufactured.  The 
founder  of  the  Krupp  iron  works  was  one  of  the  most 
determined  workers  in  this  direction,  and  although  he  did 
not  live  to  see  the  problem  solved  completely,  his  son 
succeeded  in  producing  such  perfect  cast  steel  that  Krupp's 


THE  BESSEMER  PROCESS 


271 


works  became  the  largest  iron  manufactory  in  the  world. 
These  works  employed  66,300  workmen  in  1909;  in  1910 
the  American  Steel  Trust  employed,  in  all  its  departments, 
about  205,000  workpeople. 

Cast  steel  of  this  kind  (called  crucible  steel]  leaves  nothing 
to  be  desired,  but  it  must  always  be  expensive  because  of 
the  great  number  of  processes  required  in  its  preparation  ; 
for  pig  iron  must  first  of  all  be  made  into  wrought  iron, 
and  this  must  then  be  caused  to  combine  with  carbon,  and 
finally  the  steel  must  be 
melted  in  crucibles  in  an  ex- 
tremely hot  furnace. 

Bessemer  was  the  first  to 
supply  the  world  with  cheap 
steel  very  nearly  identical  with 
crucible  steel.  In  a  lecture 
delivered  at  Cheltenham  on 
'August  1 3th,  1856,  he  made 
theastonishing  announcement 
that  steel,  which  was  costing 
from  1,000  to  1,200  marks  per 
1,000  kilos  (£50  to  £60  per 
ton),  could  be  produced  for 
from  1 20  to  140  marks  (£6 
to  £7  per  ton).  Bessemer's  process  converts  molten  pig  iron 
into  cast  steel  "without  the  consumption  of  fuel."  While  a 
puddling  furnace  changes  about  3,000  kilos  of  pig  iron  into 
wrought  iron  in  twenty-four  hours  with  the  expenditure  of 
much  coal,  the  Bessemer  process  effects  the  same  change  of 
pig  iron  to  wrought  iron,  and  to  steel,  in  fifteen  minutes. 

For  this  purpose  Bessemer  brings  the  melted  pig  iron  into 
a  pear-shaped  vessel,  provided  at  the  bottom  with  a  row  of 
pipes  for  blowing  in  air  (see  fig.  23).  The  vessel  [which 


Fig.  23. 


272  CHEMISTRY  IN   DAILY  LIFE 

is  called  a  "  converter  "]  is  constructed  of  iron  plates  riveted 
together,  and  to  enable  it  to  resist  the  high  temperature 
attained  in  the  process  it  is  lined  with  an  extremely  fire- 
resisting  material,  which  for  long  consisted  almost  wholly  of 
silicic  acid. 

The  converter  is  inclined  horizontally  [it  rotates  on 
trunnions  fixed  on  both  sides  somewhat  lower  than  the 
middle  of  the  vessel]  and  the  melted  pig  iron  is  run  into 
it,  and  while  it  is  being  brought  into  the  vertical  position 
air  is  blown  in  through  the  pipes  in  the  bottom.  The  red-hot 
carbon  *  in  the  glowing  iron  at  once  begins  to  burn,  and  this 
combustion  raises  the  temperature  to  1800°  or  2000°  C. 
[3300°  to  3600°  F.]  and  keeps  the  contents  of  the  converter 
melted.  After  about  ten  minutes  the  carbon  is  all  burnt 
off,  and  the  contents  of  the  converter  would  be  valueless 
were  not  sufficient  pig  iron  added,  at  this  moment,  to 
supply  just  enough  carbon  to  convert  the  whole  mixture  into 
steel. 

The  iron  that  is  added  for  the  purpose  of  supplying  carbon 
is  purposely  selected  because  of  its  richness  in  manganese,  an 
element  that  is  closely  allied  to  iron,  for  the  presence  of  man- 
ganese exerts  a  beneficial  effect  on  the  product  in  a  way  that 
we  cannot  inquire  into  here.  The  word  spiegeleisen  t  is  often 
met  with  ;  it  is  the  especial  name  for  a  kind  of  pig  iron  that 
contains  manganese  and  shows  a  lustrous  surface  when 
broken. 

Manganese  is  manufactured  in  some  of  the  metal  smelting 
works  to-day  for  the  purpose  of  being  used  in  the  Bessemer 

*  And  also  the  silicon  which  gets  into  the  iron  in  the  processes  that 
occur  in  the  blast  furnace  ;  for  at  the  high  temperature  of  that  furnace  a 
little  silicic  acid,  which  consists  of  silicon  and  oxygen,  is  reduced  to 
silicon,  which  dissolves  in  the  iron. 

t  Sparkling  iron ;  the  German  term  is  generally  used  in  English 
books.— TR. 


DEPHOSPHORISING  OF  IRON  273 

process,  for  this  metal  taken  alone  has  not  as  yet  found  any 
industrial  applications. 

The  Bessemer  process  enables  steel  to  be  manufactured  on 
a  very  large  scale,  for  a  single  converter  will  contain  from 
10,000  to  16,000  kilograms  [approximately  10  to  16  tons]  of 
pig  iron,  and  the  whole  of  this  is  converted  into  steel  in  a 
quarter  of  an  hour. 

Before  leaving  the  Bessemer  process  we  must  say  a  little 
regarding  the  dephosphorising  of  iron,  a  process  which  should 
further  cheapen  the  cost  of  steel. 

Most  of  the  iron  ores  that  are  found  native  contain  phos- 
phorus. The  pig  iron  that  is  made  from  such  ores  also 
contains  phosphorus,  and  unless  the  quantity  of  phosphorus 
is  extremely  small  this  iron  is  of  a  poor  quality,  and  is  only 
fitted  for  making  the  coarsest  sorts  of  cast-iron  ware  in  which 
no  great  durability  is  looked  for ;  such  pig  iron  could  not 
possibly  be  worked  up  into  wrought  iron  or  steel.  The 
analyses  of  pig  iron  made  between  1830  and  1840  showed 
that  the  unsuitability  of  certain  pig  irons  for  making  steel  or 
wrought  iron  was  connected  with  the  presence  of  phosphorus 
in  them.  At  that  time  no  method  was  known  for  keeping 
the  phosphorus  contained  in  the  ores  out  of  the  pig  iron 
during  the  processes  that  go  on  in  the  blast  furnace  ;  nor 
has  any  method  yet  been  discovered. 

Notwithstanding  the  almost  constant  attempts  to  de- 
phosphorise iron  no  result  worthy  of  mention  was  obtained 
until  Thomas  and  Gilchrist  finally  solved  the  problem  in  the 
most  ingenious  way. 

Many  investigations  had  proved  that  the  original  Bessemer 
process  did  not  remove  a  trace  of  phosphorus  from  the  iron 
used.  All  the  phosphorus  in  the  pig  iron  employed  remains 
in  the  steel  that  is  produced,  and  therefore  in  the  rails,  or  the 
axles,  or  the  surgical  instruments,  etc.,  made  of  that  steel. 
18 


274  CHEMISTRY  IN   DAILY  LIFE 

As  regards  rails,  one-tenth,  or  at  the  outside  two-tenths, 
of  a  per  cent,  of  phosphorus  might  be  permitted  ;  but  for  all 
other  applications  of  steel  the  presence  of  even  the  tenth  of 
that  quality  is  quite  out  of  the  question. 

The  raw  material  suitable  for  the  old  Bessemer  process, 
which  is  dependent  on  the  use  of  iron  ores  free  from 
phosphorus,  is  found,  as  far  as  European  interests  are  con- 
cerned, only  in  the  red  iron  ores,  containing  no  phosphorus, 
which  occur  in  Cumberland  and  Westmoreland,  in  Spain, 
Algeria,  Sweden,  Styria,  and  in  the  district  around  Siegen. 

An  immense  sensation  was  produced  among  those  con- 
nected with  the  iron  industry  by  the  announcement,  in  1879, 
that  pig  iron  containing  phosphorus  had  been  converted 
into  steel  free  from  phosphorus  in  the  Bessemer  converters 
of  Bolckow,  Vaughan  &  Co.,  the  largest  ironworks  of  the 
Cleveland  district. 

Before  the  discovery  of  the  Bessemer  process  the  rails  that 
were  manufactured  for  railways  were  made  of  wrought  iron, 
because  steel  rails  could  not  be  procured  easily  ;  but  this  was 
completely  changed  by  that  discovery,  Because  of  their 
much  greater  durability,  the  steel  rails  that  are  turned  out  so 
cheaply  by  the  Bessemer  process  have  completely  taken  the 
place  of  the  iron  rails  that  were  formerly  used. 

A  large  steel  rail  industry  sprang  up  in  Cumberland,  but 
this  industry  did  not  flourish  in  Cleveland,  where  the  iron  ores 
are  unsuited  for  making  this  kind  of  steel  because  of  the 
phosphorus  they  contain.  And  the  manufacture  of  wrought 
iron  rails  which  had  been  carried  on  in  places  where  the 
local  ores  contained  very  small  quantities  of  phosphorus, 
had  to  be  abandoned,  because  the  use  of  such  rails  was  being 
gradually  dropped  by  the  railway  companies,  who  were  more 
and  more  favouring  the  employment  of  steel  rails. 


DEPHOSPHORISING  OF  IRON  275 

The  Cleveland  manufacturers  then  determined  that  they 
also  would  manufacture  steel  rails,  and  that  they  would  turn 
their  great  appliances  to  the  best  account  by  making  use 
of  Spanish  ores  which  contained  no  phosphorus.  So  they 
manufactured  pig  iron  for  making  Bessemer  steel  from  these 
ores,  and  their  undertaking  was  crowned  with  success. 

But  the  Cleveland  iron  masters  were  not  satisfied  ;  they  set 
themselves  with  determination  to  solve  the  problem  of  finding 
a  method  which  would  allow  them  to  use  in  the  Bessemer 
process  the  iron  ores  that  were  so  plentiful  in  their  district, 
which  were  indeed  almost  lying  at  their  door.  And  the 
technical  chemists,  Thomas  and  Gilchrist,  whose  names  have 
been  mentioned  before,  succeeded  at  last  in  the  following  way. 

We  laid  stress  on  the  fact  that  in  order  to  make  his 
converter  withstand  the  action  of  heat,  Bessemer  lined  it 
with  a  very  fire-resisting  material  which  contained  much 
silicic  acid,  and  which  in  a  chemical  sense  was  therefore  acid. 
Thomas  and  Gilchrist,  on  the  other  hand,  lined  the  converter 
with  a  basic  lining  which  contained  much  lime. 

At  the  high  temperature  which  is  attained  in  the  converter 
the  carbon  of  the  pig  iron  is  burnt,  as  we  have  seen ;  and, 
as  we  should  expect,  the  phosphorus  is  also  burnt,  and  burnt 
to  phosphoric  acid.  But  whereas  in  the  original  process  this 
phosphoric  acid  remained  in  the  molten  mass,  in  the  modified 
process  it  is  able  to  combine  with  the  basic  lining,  it  enters 
into  union  with  the  lime  and  forms  phosphate  of  lime.  And 
so  the  problem  of  dephosphorising  iron  in  the  Bessemer 
converter  was  solved.  The  pig  iron  that  contained  phos- 
phorus yields  steel  that  is  free  from  phosphorus,  because  the 
phosphorus  is  held  fast,  as  phosphoric  acid,  by  the  basic 
lining. 

When  the  phosphate  of  lime  formed  in  the  linings  is  finely 
ground  it  forms  what  is  known  as  Thomas's  phosphate 


276  CHEMISTRY  IN   DAILY  LIFE 

powder,  and  is  used  by  farmers  for  manuring  meadow  land 
(see  p.  45).  And  thus  it  is  that  the  phosphorus  which  was 
formerly  so  harmful  becomes  saleable  in  this  form,  and  so 
bears  its  part  in  reducing  the  cost  of  steel.  The  fact  that 
iron  ores  containing  phosphorus  are  cheaper,  because  they 
are  obtainable  all  over  the  world,  than  those  that  are  free  from 
phosphorus,  also  tends  in  the  direction  of  cheapening  steel. 

It  must  not  be  supposed,  as  might  perhaps  be  imagined 
from  what  has  been  said,  that  the  process  of  these  fortunate 
inventors  fell  into  their  hands  from  the  skies.  On  the 
contrary,  it  was  the  fruit  of  year-long  labours  and  at  least 
a  decade  of  arduous  exertion.  The  preparation  of  a 
sufficiently  fire-resisting  basic  lining  for  the  converter  alone 
consumed  the  labour  of  many  years  and  a  large  expenditure 
of  money  before  it  was  possible  to  be  certain  that  the  con- 
siderations which  had  led  to  the  choice  of  this  material  would 
prove  themselves  workable  on  the  large  scale. 

Inasmuch  as  most  epoch-making  discoveries  are  the 
products  of  many  years  of  toil,  and  are  not  as  a  rule  isolated 
brilliant  ideas,  it  often  happens  that  disputes  about  priority 
arise  after  these  discoveries  become  known.  Thus  we  find 
that  the  idea  of  using  a  basic  lining  in  the  Bessemer  con- 
verter for  the  purpose  of  removing  phosphorus  was  suggested 
in  the  literature  pertinent  to  these  subjects  in  various 
countries  in  1875  and  again  in  1878.  But  it  seems  to  have 
been  regarded  as  an  impracticable  undertaking ;  yet  the 
question  was  solved  in  1879  m  tm's  verv  wav  'm  England. 

There  is  another  ancient  method  for  changing  pig  iron 
into  wrought  iron.  It  is  a  difficult,  and  therefore  expensive 
process  to  make  of  wrought  iron  such  objects  as  the  angle- 
pieces  and  T-pieces  that  are  required  for  leading  gas  into  living 
rooms,  keys,  door-  and  window-fastenings,  and  so  on.  Such 


SOFT  STEEL — GAS  GENERATORS  277 

small  objects  are  made  of  pig  iron,  and  are  then  packed 
between  layers  6f  iron  oxide  (natural  iron-ore  is  used)  in 
fire-resisting  boxes,  in  which  they  are  heated  for  from  ten  to 
twenty  days.  The  oxygen  of  the  iron  oxide  reacts  with  the 
carbon  in  the  pig  iron,  and  burns  it  away.  When  the  objects 
are  taken  out  of  the  boxes  they  contain  so  little  carbon  that 
they  have  the  properties  of  wrought  iron ;  they  can  be  worked 
as  wrought  iron  is  worked. 

Another  and  quite  different  method  for  making  steel  may 
be  supposed  possible.  Pig  iron  contains  more  than  2*3  per 
cent,  of  carbon,  and  wrought  iron  contains  about  £  per  cent.  ; 
if  a  mixture  of  these  two  in  the  proper  proportions  were 
melted,  a  mean  product  which  would  have  the  composition 
of  steel  would  be  obtained. 

The  difficulty  that  for  a  long  time  prevented  the  carrying 
of  this  idea  into  practice  was  that  no  reverberatory  furnace 
could  be  constructed  to  give  a  sufficiently  high  temperature 
to  effect  the  solution  of  wrought  iron,  which  is  infusible  in  an 
open  furnace,  in  molten  pig  iron  so  as  to  produce  steel. 

The  French  manufacturer,  Martin,  was  the  first  to  produce 
this  soft  steel  \  but  Siemens  had  constructed  furnaces  in  188$ 
wherein  such  steel  could  easily  be  prepared. 

In  speaking  of  puddling,  we  mentioned  that  that  process 
had  remained  essentially  unchanged  since  Cort's  discovery, 
except  as  regards  methods  of  heating  the  furnaces.  Only 
those  very  good,  and  therefore  expensive,  sorts  of  coal  which 
burn  with  a  long  flame  could  be  used  in  the  puddling 
furnaces,  as  it  was  necessary  that  the  heat  should  be  obtained 
from  the  flames  which  shot  out  from  the  grate  over  the  fire 
bridge.  But  nowadays  the  heating  is  done  by  gas,  which  is 
produced  on  the  spot  from  what  are  called  generators. 


CHEMISTRY  IN   DAILY  LIFE 

For  the  purpose  of  heating  by  gas,  fuel,  which  need  not 
be  of  first-rate  quality,  is  shot  from  a  height  on  to  a  grate. 
Under  these  conditions  the  quantity  of  air  in  contact  with  the 
fuel  is  not  sufficient  to  burn  the  carbon  completely  to  carbonic 
acid,  and  therefore  carbon  monoxide  and  other  combustible 
gases  escape  from  the  generator.*  It  must  be  noticed  that 
the  whole  of  the  nitrogen  in  the  air  that  enters  the  furnace 
through  the  grate  is  found  in  the  gases  which  escape  from 
the  generator. 

The  chief  difference  between  such  generator-gas  and 
ordinary  coal-gas,  the  latter  of  which  is  obtained  by  heating 
coal  in  closed  retorts  (see  p.  28),  is  that  the  coal-gas  does 
not  contain  nitrogen  and  consists  only  of  combustible  gaseous 
substances. 

The  hot  gases  which  come  from  the  generator  are  burnt 
in  reverberatory  furnaces  into  which  air  is  conducted.  The 
gases  pass  through  passages  in  the  walls  of  the  generator 
whereby  they  are  heated. 

Mond  has  introduced  generators  for  using  the  poorer  sorts 
of  bituminous  coal.  Steam  is  passed  continuously  through 
the  generators,  whereby  a  very  cheap  gas  is  obtained,  which 
is  useful  as  a  source  of  power  in  many  industries.  These 
generators  made  it  possible,  in  1909,  to  solve  the  problem  of 
using  peat  for  technical  purposes.  Peat  containing  from 
45  to  60  per  cent,  of  water  can  be  converted  directly  into 
heating  gas  in  these  generators,  and  the  simultaneous  recovery 
of  the  nitrogen  of  the  peat  in  the  form  of  ammonia  serves  to 
reduce  the  cost  of  the  gas.  The  enormous  quantities  of  peat 
in  various  countries  may  now  be  advantageously  used.  All 
former  attempts  to  use  peat  on  a  large  scale  involved  the 
removal  of  the  water  from  the  peat  before  using  it  as  a  com- 

*  The  reactions  have  been  more  thoroughly  described  in  the  note 
on  p.  260. 


REGENERATORS  279 

bustible  material,  and  this  preliminary  treatment  made  the 
processes  uneconomical. 

The  most  important  improvement  in  turning  to  the  best 
advantage  the  gases  made  in  generators  consists  in  the  use  of 
the  regenerators  introduced  by  Siemens.  When  the  gas  had 
done  its  work  in  gas  furnaces,  that  is,  had  heated  the  substances 
to  be  heated,  the  hot  mixture  of  the  products  of  combustion 
used  to  be  allowed  to  escape  by  the  chimney.  But  the 
regenerators  retain  the  heat  of  the  burnt  gas.  For  this  end, 
the  burnt  gas,  which  seems  to  have  fulfilled  its  special 
purpose,  is  led  through  chambers  which  are  built  with  cross- 
bars made  of  fireclay  bricks,  and  it  is  not  until  it  has  given 
up  its  heat  to  these  chambers,  which  are  thereby  raised  to  a 
full  red  heat,  that  it  is  allowed  to  escape  by  the  chimney. 
These  red-hot  chambers  form  the  regenerator.  When  the 
gas  leaves  the  generator  in  which  it  has  been  produced  it 
passes  through  the  red-hot  chambers  of  the  regenerator,  and 
is  thus  made  very  hot,  and  it  is  then  allowed  to  come  into 
the  reverberatory  furnace,  where  it  meets  with  sufficient  air 
to  burn  it  The  air  also  is  passed  through  a  red-hot  re- 
generator before  it  enters  the  furnace,  and  carries  with  it 
into  the  furnace  the  heat  which  it  has  taken  up  in  its 
passage. 

As  the  chambers  of  the  regenerator  can  be  connected  and 
disconnected  by  means  of  valves,  they  can  be  heated  in  turns 
so  that  red-hot  chambers  are  always  ready  for  heating  both 
the  gases  and  the  air,  and  as  soon  as  these  chambers  have 
given  up  their  heat  they  can  be  heated  again.  The  saving 
of  fuel  effected  by  this  method,  as  compared  with  the  old 
processes,  amounts  to  from  40  to  50  per  cent.  In  the  year 
1895  Siemens  made  further  improvements,  which  increased 
the  efficiency  of  the  regenerators.  All  the  burnt  gas  escaped 


280  CHEMISTRY  IN   DAILY   LIFE 

through  the  chimney ;  that  is  to  say,  all  the  carbon  in  the 
gas  passed  away  as  carbonic  acid.  Siemens  made  the  com- 
pletely burnt  hot  gas,  mixed  with  the  air  which  made  possible 
the  combustion  in  the  generators,  pass  again  through  the 
generators,  where  it  came  into  contact  with  burning  coal, 
wherewith  it  reacted  to  give  combustible  carbon-monoxide, 
which  afterwards  could  be  used  in  the  furnace  for  obtaining 
high  temperatures. 

Notwithstanding  the  application  of  generators  and  re- 
generators to  reverberatory  furnaces,  it  was  still  impossible 
to  manufacture  soft  steel  or  soft  iron  (for  these  are  the  names 
given  to  the  steel  produced  by  melting  together  wrought  and 
pig  iron)  in  such  furnaces.  The  open  flame  furnaces  invented 
by  Siemens  made  this  possible  for  the  first  time.  From 
theoretical  considerations  on  the  nature  of  flame,  Siemens 
came  to  the  conclusion  that  if  the  full  heating  effect  of  a 
flame  is  to  be  obtained  the  flame  ought  not  to  play  on  the 
walls  of  a  furnace,  but  must  burn  in  the  reverberatory  furnace 
itself  in  the  form  of  an  enormous  tongue.  Until  the  year 
1885  the  flame  was  arranged  so  that  it  filled  the  furnace  as 
nearly  as  might  be  ;  but  the  size  of  the  flame  has  now  been 
increased,  and  the  success  attained  has  been  very  remarkable. 
The  temperature  of  the  furnaces  has  been  raised  to  such  a 
height  that  the  best  fireclay  bricks  can  scarcely  resist  it,  and 
soft  steel  or  soft  iron  can  be  produced  with  comparative  ease. 

In  working  the  Siemens-Martin  process,  the  furnaces  were 
at  first  lined  with  material  which  was  acid  in  the  chemical 
sense.  At  a  later  time  a  basic  lining  was  used,  and  raw 
material  containing  phosphorus  was  dephosphorised  in  the 
process.  Since  1899  the  process  has  been  made  continuous. 
For  a  time  it  seemed  that  the  Thomas  process  and  the  basic 
Siemens-Martin  process  would  be  dangerous  competitors 


SOFT  STEEL  28 1 

against  one  another  in  the  manufacture  of  the  two  kinds 
of  soft  iron.  But  this  anticipation  has  been  disproved  ;  the 
two  processes  act  as  supplementary  to  each  other ;  the 
question  of  which  soft  iron  i?  to  be  preferred  is  determined 
by  the  special  purposes  of  the  user.  The  soft  iron  produced 
by  the  basic  Siemens-Martin  process  is  so  excellent,  so  easily 
worked,  that  it  has  become  a  very  dangerous  competitor 
against  wrought-iron  produced  by  the  ordinary  puddling 
process.  For  making  the  soft  iron,  old  pig  iron  and  old 
wrought  iron  can  be  melted  together  ;  hence  the  Siemens- 
Martin  soft  iron  is  produced  very  cheaply.  The  more 
expensive  iron  made  by  puddling  may  be  driven  out  of 
the  market  by  the  newer  process.  In  Upper  Silesia  puddling 
has  almost  ceased  since  1910. 

We  have  now  become  acquainted  with  the  development 
of  the  iron  industry  up  to  the  present  time.  Something  will 
be  said  in  the  next  lecture  about  the  production  of  steel  in 
electric  furnaces. 

The  methods  of  extracting  such  other  metals  as  copper, 
lead,  nickel,  etc.,  reduce  themselves  finally  to  converting  the 
naturally  occurring  ores  into  oxides  and  reducing  these  by 
means  of  carbon.  Zinc  and  aluminium  are  the  only  two 
common  metals  not  obtained  in  this  way  which  we  need 
speak  of. 

Their  beautifully  variegated  copper  roofs  form  part  of  the 
ornamentation  of  many  old  buildings,  such  as  churches  and 
castles.  When  we  wish  to  cover  spaces  nowadays  with  metal 
plates — and  this  is  done  much  more  than  it  used  to  be — we 
almost  always  employ  sheets  of  zinc,  which  are  used  chiefly 
because  they  are  so  much  cheaper  than  copper,  although  it 
must  be  admitted  that  after  a  time  they  acquire  an  unpleasing 


282  CHEMISTRY   IN    DAILY   LIFE 

grey  colour.  As  it  is  only  about  a  hundred  years  since  the 
art  of  making  zinc  plates  arose,  it  was  impossible  to  use  zinc 
as  a  covering  material  in  the  olden  days. 

The  reason  why  metallic  zinc  has  been  manufactured  only 
in  recent  times  is  as  follows.  If  a  mixture  of  oxide  of  zinc 
and  carbon  is  heated,  reduction  certainly  takes  place  with  the 
formation  of  zinc  and  carbon  monoxide,  but  the  temperature 
whereat  this  reaction  occurs  is  so  high  that  the  zinc,  which  is 
a  comparatively  easily  volatilised  metal,  is  vaporised.  If  zinc 
oxide  is  heated  with  carbon  in  one  of  the  furnaces  that  were 
formerly  used  for  reducing  metals,  vapour  of  zinc  is  soon 
given  off,  but  at  the  temperature  attained  this  is  at  once 
burnt  to  oxide,  so  that  no  metallic  zinc  is  obtained  by  this 
method  of  working. 

It  was  about  the  middle  of  the  eighteenth  century  that  the 
extraction  of  zinc  began  in  Europe — the  Chinese  seem  to 
have  practised  the  art  at  an  earlier  time — by  heating  zinc 
oxide  and  carbon,  not  in  an  open  furnace,  but  in  a  retort, 
that  is  to  say,  in  a  closed  vessel,  by  means  of  a  fire  applied 
outside  the  vessel.  The  zinc  vapour  could  not  burn  under 
such  conditions,  and  the  zinc  was  obtained  in  the  form  of 
metal  which  distilled  from  the  retorts.  It  was  not,  however, 
until  the  beginning  of  the  last  century  that  the  method  of 
making  zinc  plates  from  the  very  brittle  metal  obtained  in 
the  way  described  was  discovered.  These  zinc  plates  are 
employed  nowadays  for  all  sorts  of  purposes,  and  the  dis- 
covery of  a  means  of  making  them  has  caused  the  zinc 
industry  to  assume  very  large  dimensions. 

The  properties  of  aluminium,  the  metal  most  recently 
introduced  into  daily  life,  are  very  different  from  the  properties 
of  those  metals  we  have  spoken  of  hitherto. 

Aluminium  is  the  most  widely  distributed  of  all  metals, 
and  is  found  in  the  largest  quantities  over  the  earth.  The 


ALUMINIUM  283 

oxygen  compound,  the  oxide,  of  this  metal  has  long  been 
called  alumina  by  chemists.  The  name  aluminium  is  con- 
nected with  alum  (Latin,  alumeri)  ;  alum  has  long  been 
known  to  be  a  compound  of  alumina,  namely  a  double 
sulphate  of  potash  and  alumina  (see  p.  140). 

We  also  know  that  all  the  clays  are  silicates  of  alumina 
(see  p.  212).  Every  brick  is  rich  in  this  metal,  and  every 
potsherd  would  be  the  raw  material — the  ore — from  which 
the  metal  might  be  obtained,  were  alumina  reducible  by 
carbon  in  the  way  that  many  other  metallic  oxides  are 
reduced.  But  this  is  not  the  case,  for  that  method  is  alto- 
gether barred  in  this  instance,  because  the  avidity  of  oxygen 
for  aluminium  is  greater  than  for  carbon,  and  carbon,  there- 
fore, cannot  decompose  oxide  of  aluminium. 

The  reduction  of  their  oxides  is  not  the  only  method 
whereby  metals  can  be  prepared  in  the  laboratory.  There 
are  other  methods,  some  of  which  are  very  complicated,  and 
it  was  by  one  of  these  that  aluminium  was  first  procured  in 
1827.  Attempts  have  been  made  uninterruptedly  since  the 
beginning  of  the  fifties  of  last  century  to  apply  some  of  the 
laboratory  methods  on  the  large  scale. 

The  first  experiments  which  were  conducted  with  large 
quantities  of  material  were  put  on  foot  by  Napoleon  III.  It 
was  the  time  of  the  Crimean  war,  and  he  hoped  to  be  able  to 
use  the  very  light  metal  as  armour  for  the  soldiers.  These 
investigations  led  to  improvements  ;  nevertheless  aluminium 
prepared  by  these  processes,  which  employed  only  purely 
chemical  methods,  would  have  remained  difficult  to  obtain 
and  very  costly.  The  invention  of  dynamos  suddenly  made 
it  possible  to  obtain  very  large  quantities  of  an  agent  that 
had  been  used  for  long  in  the  laboratory  in  the  production  of 
metals,  but  had  been  very  expensive  until  about  that  time  ; 
this  agent  was  electricity, 


284  CHEMISTRY   IN    DAILY   LIFE 

Until  the  introduction  of  dynamos,  the  electricity  used  for 
technical  purposes  was  obtained  from  galvanic  batteries,  the 
working  of  which  was  costly.  Electricity  was  used  in  the 
metal  industries  for  one  purpose  only,  for  the  coating  of 
cheaper  with  more  expensive  metals.  This  process,  dis- 
covered in  1839,  is  called  electro-plating.  Large  quantities 
of  silvered  goods  have  been  prepared  by  this  process  since 
the  middle  of  last  century.  The  process  is  applied  to-day 
on  a  large  scale  to  depositing  nickel  on  other  metals  ;  nickel 
so  resists  the  action  of  air  and  water  that  it  retains  its  lustre 
for  an  indefinite  time. 

We  should  say  a  word  about  the  historical  development 
of  the  subject.  The  action  of  electricity  on  chemical  com- 
pounds was  investigated  many  years  ago.  Priestley,  in  1775, 
announced  that  the  fire  (for  that  was  the  name  used  in  those 
days)  produced  by  frictional  electricity  decomposed  ammonia 
gas.  We  know  that  ammonia  is  a  compound  of  nitrogen 
and  hydrogen  (see  p.  29) ;  if  electric  sparks  are  allowed  to 
pass  through  that  gas  a  mixture  of  nitrogen  and  hydrogen 
is  produced,  after  a  time,  in  place  of  the  ammonia.  No  one 
at  that  time  could  have  imagined  that  after  about  a  hundred 
and  twenty  years  this  observation  would  place  a  new  metal, 
aluminium,  at  the  disposal  of  mankind. 

In  1782  the  discovery  was  made  that  the  electric  fire 
could  decompose  water  into  its  constituents  hydrogen  and 
oxygen,  and  in  1800  it  was  ascertained  that  not  only 
frictional  electricity,  but  also  the  galvanic  current,  which  had 
been  discovered  ten  years  before  that  time,  could  do  this. 

As  it  was  not  very  difficult  to  obtain  electric  currents  by 
the  use  of  batteries,  the  action  of  the  current  on  chemical 
compounds  was  further  investigated,  and  in  1806  the  extra- 
ordinarily light  metal  potassium,  and  soon  afterwards  also 


ALUMINIUM  285 

the  metal  sodium,  were  obtained  by  electrolysis  of  compounds 
of  these  metals. 

And  in  this  way  chemists  became  acquainted  with  two 
quite  new  metals,  which  are  not  only  lighter  than  water, 
but  have  such  affinity  for  oxygen  that  they  burn  when  they 
are  thrown  on  to  water ;  they  do  this .  by  eagerly  with- 
drawing oxygen  from  the  water  and  combining  with  it, 
and  the  heat  produced  in  this  process  is  so  great  that  the 
hydrogen,  which  is  set  free  from  the  water,  takes  fire  in 
the  air  and  causes  the  metal  to  burn  also. 

There  seems  to  be  no  practical  application  for  these  metals, 
potassium  and  sodium,  in  ordinary  life.  But  it  is  otherwise 
with  aluminium,  with  which  we  are  specially  concerned  at 
present ;  for  although  aluminium  is  a  very  light  metal,  ana 
is  obtained  only  by  means  of  electricity,  yet  it  is  quite 
unchanged  when  exposed  to  water  or  the  air,  and  therefore 
is  of  great  practical  utility. 

The  preparation  of  aluminium  was  accomplished  by  the 
aid  of  electricity  in  the  following  way,  after  a  quite  incredible 
number  of  attempts  that  ended  in  failure.  Alumina  is  thrown 
into  a  melted  mixture  of  cryolite  (see  p.  209)  and  fluorspar, 
and  an  electric  current  is  passed  into  the  fluid  mass  (see 
figure  of  electric  furnace,  p.  35)  ;  the  current  decomposes  the 
alumina  into  its  constituents  aluminium  and  oxygen  ;  the 
aluminium  melts  and  collects  at  the  bottom  of  the  furnace, 
and  the  oxygen  gas  passes  away. 

In  1855,  i  kilo,  of  aluminium  cost  1,000  marks;  in  1856, 
300  marks  ;  in  1886,  100  marks  ;  and  in  1910,  I  \  marks.  In 
the  year  1910,  50,000  tons  of  aluminium  were  produced. 
[The  cost  fell  from  about  £25  per  Ib.  in  1855  to  about  M. 
per  Ib.  in  1910.] 

The  expectations  that  aluminium  would  find  many  uses 
have  not  been  completely  realised.  When  the  metal  became 


286  CHEMISTRY  IN   DAILY  LIFE 

cheap  most  of  the  many  articles  of  daily  use  that  were  made 
of  it  at  one  time  were  forgotten.  Neither  aluminium  nor 
alloys  of  this  metal  are  applicable  to  ship-building,  because 
they  do  not  withstand  the  corrosive  action  of  sea-water. 
Aluminium  is  used  for  making  vessels  for  chemical  factories 
and  breweries ;  and  its  use  for  making  cooking  vessels  is 
increasing.  The  difficulty  of  soldering  aluminium  has  been 
overcome,  as  it  was  shown,  in  1907,  that  pieces  of  this 
metal  can  be  joined  by  autogenous  soldering  (see  p.  35). 
Aluminium  is  an  increasingly  serious  competitor  against 
copper. 


LECTURE   XII 

ALLOYS  :  Coinage— Bronze— Patina— Brass— Tombac— Talmi  gold- 
Nickel  silver— Britannia  metal— Type  metal— Nickel  steel— Rare 
metals. 

ALKALOIDS  :  Methane— Acetylene  gas— Benzene— Pyridine— Coniine— 
Quinoline — Kairine — Antipyrin — Phenacetin — Narcotine — Chloral — 
Ether — Hoffman's  drops — Chloroform — Antiseptics — lodoform— Car- 
bolic acid — Corrosive  sublimate — Salicylic  acid. 

METALS  are  used  not  only  by  themselves,  but  alloys  are 
formed  by  melting  together  several  metals,  and  the  properties 
of  some  of  these  alloys  render  them  more  valuable  for  certain 
purposes  than  their  single  constituents.  For  instance,  those 
particular  metallic  alloys  which  are  used  for  making  coins 
pass  through  our  hands  every  day.  Pure  gold,  like  pure 
silver,  is  so  comparatively  soft  that  both  would  wear  away  too 
quickly  in  commercial  transactions.  Older  coins  would  soon 
fall  off  in  their  metallic  value  compared  with  those  newly 
coined.  But  this  happens  only  to  a  very  small  extent  with 
the  coins  that  are  now  used,  inasmuch  as  copper  is  mixed 
both  with  the  gold  and  the  silver  employed  for  coinage,  for 
experience  has  shown  that  a  sufficiently  hard  alloy  is  thus 
produced.  The  alloy  of  which  German  gold  coins  are  made 
consists  of  900  parts  of  gold  and  100  parts  of  copper  melted 
together.  As  0*3584  gram  of  gold  forms  the  coinage  unit, 
under  the  name  of  a  mark,  a  lo-mark  piece  weighs  3-982 
grams  (3-584  grams  gold  +  0*398  gram  copper).  German 


288  CHEMISTRY  IN  DAILY  LIFE 

silver  coinage  is  made  from  an  alloy  of  900  parts  of  silver 
and  100  parts  of  copper,  and  200  marks  are  coined  from 
i  kilogram  of  silver.  No  heed  is  taken  of  the  intrinsic  value 
of  the  silver,  nor  of  the  fluctuations  in  this  value,  for  gold  is 
the  standard.  One  kilogram  of  silver  is  at  present  worth 
about  72  marks.  The  German  nickel  coins  are  struck  from 
an  alloy  of  I  part  of  nickel  with  3  parts  of  copper,  and  in 
a  lO-pfenning  piece  there  are  I  gram  of  nickel  and  3  grams 
of  copper.  The  German  bronze  coinage  alloy  consists  of 
95  parts  of  copper,  4  parts  of  tin,  and  I  part  of  zinc,  and 
300  2-pfenning  pieces  or  500  i-pfenning  pieces  weigh  I 
kilogram.* 

The  mention  of  the  bronze  coinage  leads  naturally  to  the 
consideration  of  bronze  and  brass. 

Bronze  t  is  a  mixture  of  copper  and  tin  in  which  the  copper 
always  preponderates.  It  is  the  most  ancient  of  all  known 
mixtures  of  metals.  Most  investigators  are  of  opinion 
that  all  the  metallic  utensils  that  men  used  before  the 
discovery  of  a  method  for  extracting  iron  were  made  of 
bronze  ;  hence  it  is  customary  to  speak  of  the  bronze  period^ 
which  certain  people  think  was  preceded  by  a  period  of 
copper. 

Bronze  is  still  manufactured  in  very  large  quantities,  and  it 
is  employed  for  all  sorts  of  purposes.  Not  only  as  church 
bells  does  it  send  its  warning  sound  to  the  ears  of  the  solitary 
man,  but  also  in  the  form  of  cannon,  which  only  began  to  be 

*  The  English  gold  coinage  alloy  consists  of  1 1  parts  of  gold  and  i  of 
copper  ;  the  silver  coinage  alloy  of  H  of  silver  and  -fa  of  copper ;  and  the 
bronze  coinage  alloy  of  95  parts  of  copper,  4  parts  of  tin,  and  i  part  of 
zinc.— TR. 

t  According  to  the  most  recent  investigation  the  word  "  bronze  "  is 
a  contraction  derived  from  <zs  Brundusinum — that  is,  metal  from 
Brundusium  (the  modern  Brindisi) ;  just  as  as  Cyprium^  metal  from 
Cyprus,  is  the  origin  of  the  word  "copper." 


BRONZE  AND  BRASS  289 

made  of  cast  steel  a  generation  ago,  it  has  an  impressive  word 
to  say  in  determining  the  fates  of  the  peoples.  Most  lengthy 
investigations  have  been  conducted  by  different  states  all  over 
the  world  with  regard  to  tLe  bronze  alloys,  in  the  hope 
of  finding  the  absolutely  best  alloy  for  casting  cannon,  and 
the  books  that  contain  accounts  of  all  that  can  be  said  or 
thought  about  the  bronzes  would  fill  a  library.  The  remark- 
able ease  with  which  bronze  can  be  cast  makes  it  a  most 
suitable  material  for  producing  works  of  art ;  and  the  great 
equestrian  statues,  for  instance,  show  how  safely  it  can  be 
manipulated  for  such  purposes. 

Such  works  of  art  do  not  suffer  hurt  by  long  exposure  in 
the  open  air,  but  they  take  on  that  beautiful  rich  rust 
which  is  called  patina*  It  is  characteristic  of  patina  that 
along  with  its  malachite-green  colour  it  has  a  metallic 
character ;  the  peculiar  metallic  lustre  appears  through  the 
colour.  In  this  respect  it  is  entirely  different  from  any 
colouring  material ;  for  if  a  statue  is  made  lustrous  by  a  coat 
of  varnish,  for  instance,  the  gloss  is  altogether  superficial  and 
does  not  come  from  within. 

Copper  alloys  with  zinc  just  as  readily  as  with  tin.  There 
is  a  great  demand  for  brass,  which  is  the  product  of  mixing 
copper  and  zinc.  Although  zinc  was  not  isolated  until  the 
eighteenth  century  (see  p.  282),  yet  the  observation  had 
been  made  long  before  that  the  metal  obtained  by  smelting 
copper  ores  was  yellow,  and  not  red,  when  certain  other 
ores  were  added  before  smelting ;  these  other  ores  were 
called  cadmia  by  the  ancients,  and  at  a  later  time  the  name 

*  If  much  coal  lis  burnt  near  to  bronze  statues  the  sulphurous  acid 
that  is  sent  into  the  air  along  with  the  soot,  which  in  itself  is  hurtful,  so 
greatly  retards  the  formation  of  patina  that  in  many  cases  none  gets 
formed. 

19 


290  CHEMISTRY   IN   DAILY   LIFE 

calamine  was  given  to  them.  We  know  now  that  the  sub- 
stances called  cadmia  or  calamine  were  ores  of  zinc. 
Aristotle,  about  330  B.C.,  tells  that  a  kind  of  copper  was 
found  in  India  which  could  be  distinguished  from  gold  only 
by  its  taste  ;  for  whereas  it  was  very  pleasant  to  drink  out 
of  golden  vessels,  all  vessels  that  contained  copper  had  a 
disagreeable  metallic  taste.  Aristotle  recommended  this 
means  of  distinguishing  the  two  metals  as  an  analytical 
method  very  suitable  for  the  time.* 

Brass  can  be  made  to  resemble  gold  very  closely  by  using 
suitable  quantities  of  the  constituent  metals ;  and  various 
articles  made  of  this  alloy,  which  is  known  as  tombac^  came 
into  the  market.  The  addition  of  some  lead  produces  a 
colour  which  very  closely  resembles  that  of  gold,  but  the 
product  is  not  very  lasting,  as  it  soon  oxidises  in  the  air. 
By  covering  this  alloy,  or  tombac,  with  a  little  gold  the 
substance  known  as  talmi  goldis  produced. 

We  should  not  pass  over  "  cuivre  poli"  although  that 
substance  is  going  out  of  fashion.  It  is  something  between 
brass  and  bronze,  and  may  be  described  either  as  a  bronze 
rich  in  zinc  or  a  brass  poor  in  tin  ;  it  is  nearly  as  cheap  as 
brass — at  present  the  cost  of  zinc  is  something  less  than  an 
eighth  of  that  of  tin. 

Nickel  silver  is  produced  by  melting  together  copper,  zinc, 
and  nickel.  This  alloy  played  an  important  part  from  1820 
until  about  1860 ;  but  it  has  been  driven  into  the  background 

*  He  also  relates  that  the  Mesyncecians,  a  people  living  towards  the 
north,  made  copper  yellow  by  melting  it  with  a  certain  earth,  which  must 
have  been  an  ore  of  zinc.  Some  would  derive  the  [German]  word  messing 
[  =  brass]  from  the  name  of  that  people ;  others  say  it  comes  from 
moschen  or  maischen^  an  older  form  of  mischen  [to  mix] ;  and  the 
brothers  Grimm  derive  it  from  ?nassa,  a  word  used  in  the  Middle  Ages 
to  express  an  unworked  lump  of  metal. 


TYPE  METAL — NICKEL  STEEL  29! 

by  the  introduction  of  silver  electro-plated  goods.  It  was  at 
first  customary  to  strongly  plate  goods  made  of  nickel  silver. 
Cheaper  white  metallic  mixtures  were,  however,  soon  intro- 
duced as  the  material  to  be  olated — for  instance,  Britannia 
metal,  which  is  produced  by  melting  together  90  parts  of  tin 
and  10  parts  of  antimony  ;  but  this  in  turn  has  been  replaced 
by  yet  cheaper  materials. 

In  conclusion,  we  must  mention  type  metal,  which  is  an 
alloy  that  we  certainly  do  not  often  have  an  opportunity  of 
seeing,  although  it  serves  to  multiply  our  intellectual  and 
spiritual  nourishment.  Lead  is  the  chief  constituent  of  this 
alloy ;  and  to  this  are  added  antimony  and  a  little  tin  and 
other  similar  metals.  It  is  unfortunate  that  no  one  should 
have  been  able  to  produce  an  alloy  suitable  for  use  in  printing 
without  putting  lead  into  it,  because  if  this  were  done  a  final 
stop  would  be  put  to  the  serious  cases  of  chronic  lead  poison- 
ing which  are  not  uncommon  amcng  compositors. 

We  have  now  seen  what  new  valuable  properties  can  be 
given  to  such  very  useful  metals  as  copper,  zinc,  and  others 
by  alloying  them.  Iron,  which  we  considered  in  great  detail, 
is  an  exception  in  this  respect.  All  the  efforts  made  to 
improve  the  properties  of  iron  by  mixing  it  with  other 
metals  were  without  result  until  the  year  189$.  But  success 
certainly  seems  to  have  come  at  last,  especially  in  increasing 
the  hardness  of  steel  by  mixing  it  with  a  little  nickel,  in 
accordance  with  results  which  were  obtained  in  some  of  the 
French  works ;  the  hardness  of  the  best  steel  is  to  that  of 
nickel  steel  as  4  is  to  7.  Very  durable  gun  barrels  of  heavy 
calibre,  and  also  torpedo  boats,  have  been  manufactured  of 
late  years  of  nickel  steel,  and  it  has  also  been  used  for  making 
armour  plate  for  men  of  war,  notwithstanding  its  high  price. 
Nickel  steel  does  not  rust  in  sea-water;  moreover,  the  bottoms 


CHEMISTRY  IN   DAILY  LIFE 


of  vessels  made  of  this  alloy  do  not  become  foul  by  the 
growth  of  Crustacea  and  sea-weed,  so  that  the  costly  and 
tedious  process  of  docking  the  vessels  for  cleaning  is  almost 
unnecessary. 

The  invention  of  nickel  steel  has  made  possible  the 
production  of  steam  turbines,  so  much  spoken  of  nowa- 
days. These  turbines  require  to  be  furnished  with  blades 
of  2  or  3  metres  (say  2  or  3  yards)  diameter,  making  4,000 
revolutions  per  minute.  The  centrifugal  force  under  these 
conditions  would  tear  pig  iron  to  pieces  like  paper-sheets  ; 

but  the  hardness  of  nickel  steel  is 
so  great  that  blades  of  that 
material  can  bear  four  or  five 
times  this  strain.  On  account 
of  its  hardness  and  resistance 
to  disintegration,  nickel  steel  is 
also  used  in  making  parts  of  motor- 
cars. In  this  connection  steels  are 
used  which  were  not  even  thought 
of  a  few  years  ago.  The  high  price 
of  these  steels  is  of  no  importance 
compared  with  their  durability  and 

the  possibility  of  making  with  them  very  small  explosion 
machines.  Such  steels  can  be  made  only  at  the  very  high 
temperature  of  the  electric  furnace.  The  best  of  the  electric 
furnaces  for  melting  steel  is  that  introduced  by  Girod.  The 
principle  of  this  furnace  is  made  clear  by  the  figure  (24). 
The  melted  metal,  M,  is  placed  in  a  fire-resisting  vessel,  P ; 
the  metal  is  covered  with  a  layer  of  molten  slag,  S ;  by  the 
two  fixed  metallic  contact  pieces,  C,  the  current  passes  into 
the  metal,  which  is  made  one  of  the  electrodes,  and  to  the 
other  carbon  electrode,  A.  The  electric  furnace  makes 
possible  the  production  on  a  large  scale  of  steel  as  valuable 


24. 


RARE   METALS — ELECTRIC   LAMPS  293 

as  crucible  steel  (see  p.  271);  the  soft  iron  produced  in 
Bessemer  converters,  or  in  Martin  furnaces,  can  be  refined 
in  the  electric  furnace  at  a  very  high  temperature  without 
exposing  it  to  the  action  of  gases  produced  by  the  com- 
bustion of  coal  or  coke.  Addition  of  chromium,  vanadium, 
titanium,  silicon,  etc.,  can  be  made  to  the  steel  in  the  electric 
furnace,  for  the  purpose  of  producing  steel  having  special 
properties  which  fit  it  for  special  uses. 

We  have  mentioned  the  names  of  some  rare  metals.     In 
recent  years  the  names  of  several  other  rare  metals  have  come 
to  be  often  in   men's  mouths.     Electric  lighting  has  made 
people  accustomed  to  hear  of  tantalum,  tungsten,  and  osram 
lamps.     When    Edison    introduced    electric   glow   lamps   he 
used  very  fine  filaments  of  carbon  as  the  material  which  was 
raised  to  so  high  a  temperature  by  the  electric  current  that 
it   became   luminous.     It   was   necessary  to  remove  the  air 
completely  from  around  the  carbon  filament,  else  the  carbon 
would  have  been  burned  to  carbonic  acid  ;  the  filament  was 
suspended  in  a  glass  globe  from  which  all  the  air  had  been 
removed.       The    light-giving    capacity    of    such    a    carbon 
filament   is   very   unfavourably   related    to   the    quantity   of 
electricity  which    passes  through   it.     Attempts    were  made 
to  find  filaments  better  suited  for  their  purpose  than  those 
of  carbon  ;    after  working  for  twenty-five  years  the  distin- 
guished technologist  succeeded.     At  first  he  used  thin  wires 
of  metal  in  place  of  the  carbon  filaments.     The  metals  used 
in  ordinary  life,  such  as  iron,  copper,  etc.,  melt  when  they  are 
heated  by  electricity,  in  a  space  free  from  air,  until  they  glo\v. 
It  was  necessary  to  find  metals  the  melting  points  of  which 
are  so  high  that  they  do  not  melt  under  these  conditions. 
Investigations  were  made  of  metals  the  ores  of  which  occur 
only  in  relatively  small  quantities,  metals  which  had  been 


294  CHEMISTRY   IN   DAILY   LIFE 

used  only  by  chemists  in  their  laboratories  for  purely 
scientific  purposes.  These  metals  were  produced  in  larger 
quantities  for  the  first  time  in  electrical  factories,  and  their 
behaviour  was  studied  when  in  the  form  of  fine  threads. 
Many  difficulties  had  to  be  overcome  before  fine  threads 
could  be  made  of  metals  which  melt  only  at  very  high 
temperatures,  and  are  exceedingly  hard  to  work.  A  fine 
thread  of  tantalum  glows  in  the  tantalum  lamp,  of  tungsten 
in  the  tungsten  lamp,  and  so  on.  The  advantage  possessed 
by  these  lamps  is  that  they  emit  at  least  twice  as  much  light 
as  the  old  Edison  carbon  filament  lamps  when  the  same 
quantity  of  electricity  is  passed  through  them  as  through 
carbon  lamps ;  in  other  words,  they  give  as  much  light  as 
the  older  lamps  at  half,  or  less  than  half,  the  cost. 

Everything  that  has  been  brought  forward  in  these 
lectures  up  till  now  has  been  concerned  with  knowledge  which 
either  is  for,  or  can  be  applied  to,  the  advantage  of  mankind 
in  general.  We  picture  mankind  to  ourselves  as  a  whole 
constantly  striving  to  advance,  but  restricted  by  the 
conditions  of  the  time.  But  chemistry  has  also  for  long 
sought  to  place  its  results  at  the  service  of  the  individual 
who  comes,  lives,  and  departs,  and  who  during  the  short 
space  of  his  life  is  too  often  subject  to  sickness  and  laid  low 
by  illness. 

An  older  period  in  the  history  of  chemistry  is  distinguished 
as  the  time  of  the  iatro,  or  medical,  chemists.  But  the 
advances  made  in  this  direction,  as  in  so  many  others,  since 
the  year  1803  put  into  the  shade  all  that  had  gone  before. 

The  first  step  in  this  direction  was  the  discovery  of  the 
alkaloids,  which  is  the  name  given  to  certain  substances  of 
an  alkaline  character  that  are  present  in  plants.  It  was 


ALKALOIDS  295 

supposed  until  that  discovery  was  made  that  only  acids, 
such  as  tartaric  and  citric  acid  and  the  like,  and  neutral 
substances,  such  as  sugar  and  starch,  could  be  obtained  from 
the  vegetable  kingdom.  But  in  investigating  certain  medically 
active  drugs  in  1803,  Derosne  discovered  a  substance  with  an 
alkaline  reaction  to  which  he  gave  the  name  of  opium  salt. 
This  result  struck  him  as  so  remarkable  that  he  speaks  of  the 
salt  as  a  "mature  vtgeto-animale  toute  particular e"  It  was 
not  until  1817  that  pure  morphine,  an  impure  form  of  which 
constituted  the  opium  salt  of  Derosne,  was  prepared  and 
was  finally  proved  to  be  a  vegetable  substance  capable  of 
combining  with  acids  after  the  manner  of  a  true  base. 

We  need  not  now  enter  into  details  concerning  the  value 
of  such  an  alkaloid  as  quinine  as  a  febrifuge,  or  of  morphine 
as  a  sleep-giver,  or  of  atropine  for  opening  the  pupil  of  the 
eye,  or  of  cocaine  as  a  local  anaesthetic  or  a  kind  of  chloroform 
active  only  at  one  spot,  or  of  similar  alkaloids  which  to  an 
ever  increasing  extent  serve  to  alleviate  and  heal  the  troubles 
of  suffering  humanity.  It  is  true  that  before  the  alkaloids 
themselves  were  known  the  drugs  in  which  they  occur  were 
used  as  medicines  with  more  or  less  success.  But  the 
alkaloids  are  often  mixed  in  these  drugs  with  so  many 
other  substances  which  modify  their  especial  activity  that 
the  action  of  the  alkaloid  may  sometimes  be  almost  entirely 
suppressed.  This  is  the  case,  for  instance,  with  morphine, 
as  compared  with  opium  taken  directly  from  the  plant,  and 
from  which  morphine  is  extracted.  The  action  of  opium  as 
a  whole  makes  it  useful  for  certain  purposes,  but  not  for 
employment  as  a  sleep-producer.  One  kilo,  of  morphine 
costs  about  360  marks  ;  I  kilo,  of  opium  about  25  marks  [i  Ib. 
of  morphine  costs  about  £8  ;  I  Ib.  of  opium  about  IOT.]. 

The  chemical  investigation  of  alkaloids  shows,  as  we  might 


296  CHEMISTRY   IN   DAILY   LIFE 

expect,  that  the  atomic  complexes  of  which  they  consist  are 
very  far  from  being  simple.  We  have  already  learned 
(see  pp.  22  and  66),  that  in  order  to  have  clear  concep- 
tions about  a  chemical  compound  it  is  not  enough  to  know 
the  number  of  atoms  which  build  up  the  compound,  but  that 
we  must  also  disentangle  the  atoms  and  discover  how  they 
are  connected  with  one  another.  It  is  only  when  this 
problem  has  been  solved — and  even  one  who  is  not  a  chemist 
will  understand  how  extraordinarily  difficult  such  a  problem 
may  be — that  attempts  can  be  made  in  the  laboratory  to 
reverse  the  procedure,  and  that  the  task  of  building  up 
artificially  such  an  atomic  complex  from  the  single  atoms — 
that  is,  of  synthesising  the  natural  product — can  be  entered 
upon.* 

The  hydrocarbon  which  is  called  methane  or  marsh-gas 
is  composed  of  a  single  atom  of  carbon  and  four  atoms 
of  hydrogen — thus 

Hydrogen  H 

I 
Hydrogen — Carbon — Hydrogen,  or  abbreviated  H — C — H. 

Hydrogen  H 

Now  we  know  (p.  22)  that  organic  compounds  may  be 
regarded  as  derived  from  this  hydrocarbon  by  supposing 
that  other  atoms,  or  atomic  complexes,  are  substituted 
for  the  hydrogen  atoms  of  methane  [or  derivatives  of 
methane],  one  monovalent  residue  taking  the  place  of 
another  such  residue,  or  a  divalent  taking  the  place 

*  It  is  only  about  forty  years  since  the  problem  of  building  up, 
from  atoms  of  carbon,  hydrogen,  and  oxygen,  ordinary  pure  spirit,  which 
is  a  comparatively  simple  substance — its  composition  being  expressed 
(see  p.  85)  by  the  formula  C2H6O — was  solved  in  the  laboratory.  The 
alcohol  that  is  made  in  the  laboratory  is,  however,  enormously  more 
expensive  than  that  which  is  obtained  by  fermentation. 


STRUCTURE    OF    HYDROCARBONS  297 

of    a    divalent,    or    a    trivalent    the    place    of    a    trivalent 

H 
I 
residue.      The  group    H— C— ,  for  instance,  is  a  monovalent 

H 

residue  of  methane,  for  it  is  methane  minus  one  atom  of 
hydrogen.  If  this  combines  with  itself  we  have  the  molecule 

H    H 
I      I 
H— C— C— H,  which  is  the  hydrocarbon  ethane,  C2H6,  which 

I      I 
H    H 

we  have  already  become  acquainted  with  (see  p.  23). 

We  can  think  of  these  chains  of  carbon  atoms  as 
lengthened  to  any  extent,  by  repeating  the  replacement 
of  H  by  CH3  (see  p.  22),  and  also  as  branching  out  and 
even  as  returning  upon  themselves  in  the  form  of  rings. 
Let  there  be  a  hydrocarbon  consisting  of  a  chain  of  six 
atoms  of  carbon  to  each  of  which  only  a  single  atom  of 
hydrogen  is  linked  (all  the  other  linkings  compensating 
each  other  as  "double  linkings,"  represented  by  double 
lines) ;  we  shall  have  the  following : 

___         ^_.^ 

I      I      I      I      I      I 
H    H    H    H    H    H 

Parts  of  the  capacities  for  combination  of  the  two  carbon 
atoms  at  the  ends  of  the  chain  are  not  satisfied  ;  they  hang 
in  the  air,  so  to  speak.  In  1866  Kekule  (who  was  then 
Professor  of  Chemistry  at  Bonn)  made  the  memorable 
suggestion  that  the  two  carbon  atoms  at  the  ends  of  the 
chain  are  linked  one  to  another;  hence,  if  one  regards 
the  carbon  atoms  as  symmetrically  arranged,  they  are  held 


298  CHEMISTRY   IN   DAILY   LIFE 

together  in  the  form  of  a  ring.  As  it  is  inconvenient 
always  to  draw  circular  figures,  the  custom  has  been 
adopted  of  drawing  straight  lines  between  the  six  carbon 
atoms,  whereby  the  circle  becomes  a  hexagon,  a  figure 
which  is  constantly  met  with  in  chemical  literature. 

H 

H— 

H—  cC—  H 


The  hydrocarbon  represented  by  the  above  scheme  is 
the  most  simple  imaginable  under  the  conditions  laid 
down.  It  is  composed  of  six  carbon  atoms  and  six  atoms 
of  hydrogen  ;  its  formula  is  therefore  C6H6.  This  hydro- 
carbon was  discovered  in  1826  ;  the  name  benzene  is  given 
to  it,  from  benzole  acid. 

Benzene  is  found  in  considerable  quantities  in  coal  tar  ; 
it  is  the  mother  substance  of  an  enormous  number  of  com- 
pounds, among  which  may  be  mentioned  the  aniline  colours. 
The  aniline  colour  industry  could  not  have  attained  the 
flourishing  condition  it  is  now  in  without  the  conception  of 
ring-formed  atomic  complexes  ;  it  is  that  conception  which 
has  made  possible  an  explanation  of  the  chemical  behaviour 
of  the  aniline  compounds,  and  has  led  to  advances  in  their 
investigation.* 

It    has   been    known    since   the   eighties   of    last   century 

*  I  have  omitted  about  a  couple  of  pages  here,  wherein  the  author 
speaks  of  the  great  advances  made  by  German  chemists  in  the  syntheses 
of  complex  compounds,  and  quotes  from  Ostwald  a  passage  in  praise  of 
the  German  methods  of  study  as  compared  with  those  prevalent  in 
England.—  TR. 


CONIINE   AND  QUININE  299 

that  ring-formed  atomic  complexes  are  constituted  not 
only  of  atoms  of  carbon  and  hydrogen,  but  that  the 
closing  of  the  ring  can  be  brought  about  by  atoms  of 
nitrogen  also.  Nitrogen  is  represented  by  the  symbol  N, 
and  the  simplest  possible  compound  of  this  kind  is 
C5H6N. 

H 

C 

H— cr^Nc— H 


H— C'\XC— H 

N 

This  compound  is  called  pyridine}  and  is  found  in  coal 
tar.  All  the  alkaloids,  all  those  constituents  of  plants 
which  have  such  a  powerful  action  on  the  human  organism, 
with  a  few  exceptions,  are  derivatives  of  this  compound. 
Coniine,  for  instance,  the  alkaloid  of  the  poisonous  plant 
hemlock,  the  empirical  formula  of  which  is  C8H17N,  is 
represented  by  the  following  atomic  arrangement : 

H, 


H2— CXX'C— CH2— CH2— CH3 

N 

H 

The  method  of  the  arrangement  of  the  atoms  in  this 
substance  was  made  known  fully  by  Ladenburg  ;  and  this 
atomic  complex,  which  up  to  that  time  had  been  built  up 
only  by  nature  in  plants,  was  prepared  artificially  from 
pyridine  by  him  in  1888. 

The  investigation  of  quinine^  C2oH24N2O2,  the  most  cele- 
brated of  all  febrifuges,  has  been  carried  so  far  that,  since 


3oo 


CHEMISTRY   IN   DAILY  LIFE 


the  year  1909,  we  know  how  the  48  atoms  of  this  compound 
are  arranged  relatively  to  one  another.  Quinine  is  con- 
structed in  a  much  more  complicated  way  than  coniine, 
for  example.  But  quinoline  is  easily  obtained  by  splitting 
up  quinine ;  and  investigation  has  shown  that  quinoline  is 
an  atomic  complex  of  two  rings,  and  that  in  this  compound 
a  benzene  ring  and  a  pyridine  ring  are  combined  in  the  way 
represented  by  the  following  scheme  : 


H 


H— C 


H— C 


C— H 


C— H 


As  a  kilogram  of  quinine  still  costs  about  40  marks  [about 
iSs.  per  lb.],  although  the  price  has  fallen  considerably,  the 
quinoline  made  from  quinine  was  a  very  expensive  substance  ; 
but  a  kilogram  of  quinoline  can  be  bought  to-day  for  less 
than  10  marks  [about  45.  6d.  per  lb.],  because  this  alkaloid 
can  be  made  cheaply  from  coal  tar  derivatives,  so  that  it  is 
no  longer  necessary  to  use  the  expensive  quinine  for  its 
preparation. 

As  it  was  long  known  that  quinoline  is  what  one  might 
call  the  skeleton  of  quinine,  the  question  suggested  itself 
whether  it  would  be  necessary  to  clothe  this  skeleton  with 
exactly  the  same  atoms  and  atomic  complexes  as  are  con- 
tained in  quinine  in  order  to  produce  a  substance  with  the 
qualities  of  a  febrifuge  ;  whether,  if  quinoline  were  trans- 
formed into  an  arrangement  of  atoms  which,  judging  from 
the  sum  of  our  experience,  would  be  suitable,  the  new 


SLEEP-PRODUCING  SUBSTANCES  301 

substance,  although  only  roughly  approximating  to  the 
natural  product,  would  resemble  that  product  in  possessing  the 
power  of  reducing  the  bodily  temperature  of  feverish  patients. 
After  many  trials  the  first  artificial  febrifuge  made  its 
appearance  in  1881,  and  to  it  was  given  the  name  kairine. 
This  substance  has  been  replaced  by  more  active  bodies,  and 
has  long  been  forgotten,  for  since  that  time  one  new  remedy 
has  followed  hard  on  the  heels  of  another.  When  some 
knowledge  of  the  special  conditions  had  once  been  gained, 
it  was  found  that  febrifuges  could  be  prepared  by  putting 
together  much  simpler  complexes  of  atoms  than  quinoline, 
and  so  it  became  easier  to  make  such  bodies  in  the  laboratory. 
The  two  substances  which  have  proved  to  be  the  most 
practically  useful  are  antipyrin,  the  atomic  arrangement  of 
which  is  very  complicated,  but  which  is  not  a  derivative 
of  quinoline,  and  pJunacetin,  a  body  with  a  comparatively 
simple  arrangement  of  atoms. 

We  have  already  mentioned  morphine,  the  introduction 
of  which  sleep-producing  substance  marked  an  epoch  in  the 
advance  of  therapeutical  medicine,  beginning  with  1855,  when 
Wood  first  used  subcutaneous  injections  of  the  alkaloid,  and 
so,  by  sending  it  directly  into  the  blood,  made  its  action 
quicker  and  more  trustworthy. 

Very  many  attempts  have  been  made  to  find  a  suitable 
substitute  for  morphine  because  of  the  danger  of  that  craving 
for  it  which  is  apt  to  follow  the  use  of  this  drug.  The  first 
substitute  was  chloral,  which,  as  its  name  suggests,  bears 
some  chemical  relation  to  chloroform. 

As  time  has  gone  on  the  number  of  these  substitutes  for 
morphine  has  become  legion,  for  it  has  been  found  that 
substances  of  the  most  different  kinds  have  this  common 
property  of  producing  sleep.  Common  alcohol  is  a  sleep- 


302  CHEMISTRY  IN   DAILY  LIFE 

producer ;  but  the  use  of  it  in  quantity  is  apt  to  be  followed 
by  unpleasant  effects  on  the  next  day  ;  and  it  is  the  same 
with  many  of  the  drugs  that  have  been  introduced  recently  ; 
they  produce  sleep,  it  is  true,  but  they  also  produce  many 
unpleasant  effects.  The  number  of  those  soporifics  that  are 
effective  has  diminished  of  late  years  ;  but  there  are  still  too 
many  of  these  drugs  in  use. 

While  the  special  purpose  of  these  sleep-producers  is  to 
induce  a  sleep  which  as  closely  as  possible  simulates  natural 
sleep,  it  is  also  well  known  that  there  are  substances  which 
produce  so  deep  an  unconsciousness  that  the  most  severe  opera- 
tions can  be  performed  without  the  patient  feeling  any  pain. 

The  first  substance  to  be  employed  for  this  purpose  was 
ether,  a  body  that  is  easily  prepared  from  alcohol.  As  ether  is 
more  conveniently  obtained  by  distilling  alcohol  with  sulphuric 
acid,  it  used  to  be  called,  and  is  still  popularly  called, 
sulphuric  ether>  although  it  does  not  contain  a  trace  of  sulphur, 
a  fact  which  has  been  known  for  about  a  hundred  years. 

Ether  was  discovered  about  1530  by  Valentinus  Cordus, 
who  was  Professor  of  Medicine  at  Wittenberg ;  and  as  early 
as  1541  its  sleep-producing  properties  were  known  to 
Theophrastus  Paracelsus  Bombastus.  In  one  of  his  books  * 
he  says  f  :  "  This  sulphur  "  (he  means  ether)  "  has  an  attraction 
for  others ;  fowls  take  it  and  sleep  for  a  time,  waking  again 
without  any  hurt."  \ 

*  Vol.  i.,  p.  1064,  of  the  complete  reprinted  works  of  Paracelsus, 
published  at  Strassburg  in  1603. 

t  "Zum  andern  hatt  dieser  Sulphur  eine  Siisse,  dass  jhn  die  Hiihner 
all  essen,  vnd  aber  endtschlaffen  auff  ein  Zeit,  ohn  schaden  wieder 
auffstohndt." 

J  In  another  part  of  the  same  book  Paracelsus  extols  ether  as  a 
remedy  in  all  complaints.  Hoffman,  a  clinical  physician  of  Halle, 
about  1750  strongly  recommended  a  mixture  of  three  parts  spirit  with 
one  part  ether  as  a  soothing  and  pain-stilling  drug,  and  the  mixture 
became  a  popular  remedy  under  the  name  of  Hoffman's  drops. 


ANESTHETICS  303 

Three  hundred  years,  unfortunately,  passed  before  the 
full  importance  was  appreciated  of  the  experiment  on  animals 
made  by  Paracelsus,  which  proved  that  a  deep  sleep  from 
which  one  awoke  without  harm  could  be  produced  by  ether  ; 
and  this  is  greatly  to  be  regreited,  for  much  of  the  pain  that 
was  borne  for  centuries  by  suffering  humanity  might  have 
been  alleviated,  and  operations  might  have  been  performed 
painlessly  during  all  these  three  hundred  years. 

An  American  chemist,  Jackson,  was  the  first  fully  to 
appreciate  the  importance  of  ether  as  an  anaesthetic  ;  in 
1846  he  recommended  a  dentist  of  the  name  of  Morton  to 
use  it  during  operations  on  the  teeth.  The  results  were  so 
remarkable  that  Warren,  a  surgeon,  to  whom  they  had  been 
communicated,  on  October  I7th,  1846,  ventured  to  operate 
on  a  patient  who  had  been  made  entirely  unconscious  by 
ether.  The  painless  performance  of  surgical  operations  dates 
from  that  day. 

A  search  began  at  once  to  be  made  for  specifics  which 
should,  if  possible,  be  more  suitable  for  bringing  about  the 
desired  effect  than  the  very  explosive  ether — the  application 
of  an  actual  cautery,  for  instance,  was  impossible  when  ether 
was  employed  ;  and  as  early  as  1847  Simpson  recommended 
chloroform,  which  has  held  the  field,  on  the  whole,  since  that 
time,  although  attempts  have  been  constantly  made  to  replace 
it  by  other  and  more  efficient  substances,  or  mixtures  of 
substances. 

Chloroform  was  prepared  for  the  first  time  in  1831  by 
Liebig  from  chloral  ;  it  is  manufactured  to-day  by  the 
action  of  chloride  of  lime  on  alcohol.  Chemically  considered 
chloroform  is  a  very  simple  substance.  If  three  atoms  of 
hydrogen  in  the  hydro-carbon  methane,  with  which  we  are 
now  so  familiar,  are  replaced  by  chlorine — and  this  can  be 


304  CHEMISTRY  IN   DAILY  LIFE 

done  directly  in  the  laboratory — we   have   chloroform   pro- 
duced. 

H 
H— C— H 

H 

Methane. 
Chlorine  Cl 

I  I 

H—C— Chlorine,  or  abbreviated  H— C— Cl 

I  I 

Chlorine Cl 

"**" Chloroform.       "~  ' 

Iodine  I 

I  I 

H—C— Iodine,   or  abbreviated   H—C— I 

Iodine I 

lodoform. 

In  the  above  formulae  iodoform  is  placed  beneath  chloroform, 
to  which  it  is  closely  allied.  The  abbreviated  termination 
form  is  derived  from  the  name  formic  acid ;  for  the  chemical 
constitution  of  these  compounds  is  related  to  that  of  this 
acid,  which,  like  them,  is  a  derivative  of  methane  very  closely 
related  to  the  parent  compound. 

In  associating  iodoform  with  chloroform  we  have  passed 
from  the  class  of  narcotics  to  that  of  antiseptics,  which  have 
added  the  equable  and  regular  healing  of  wounds  to  the 
painlessness  wherein  chloroform  has  enveloped  the  operations 
of  the  surgeon. 

The  world  owes  this  improvement  in  the  treatment  of 
wounds,  the  greatest  of  its  kind  ever  made,  to  Lister,  whose 
genius  was  turned  in  this  direction  by  the  work  of  Pasteur 
on  the  lowest  forms  of  living  things. 

When  the  bacteria  which  are  present  everywhere  in  the  air 
get  into  wounds  they  cause  suppuration,  and  they  often  also 
bring  about  other  bad  results  which  are  extremely  dangerous 


ANTISEPTICS  305 

and  sometimes  fatal.  As  it  is  impossible  to  shut  out  the 
surrounding  air  from  contact  with  a  wound,  care  has  been 
taken,  since  this  method  was  introduced  about  the  middle 
of  1870,  to  dress  the  wound  with  some  substance  capable  of 
killing  the  bacteria  in  the  surrounding  air.  Carbolic  acid  is 
the  substance  that  Lister  used  for  this  purpose. 

In  well-appointed  hospitals  one  goes  a  step  further. 
Instead  of  trusting  to  antiseptics,  the  aseptic  method  is  used  ; 
that  is  to  say,  the  instruments  are  boiled  in  order  to  kill 
bacteria,  the  overalls  of  the  operator  are  sterilised  in  a  current 
of  steam,  his  hands  are  freed  from  bacteria  by  washing  in 
alcohol,  and  the  surfaces  of  the  patient's  skin  are  treated  in  a 
similar  way,  the  bandages  are  made  of  sterilised  wool,  and  so 
on.  This  treatment  obviates  contact  of  the  patient  with 
antiseptics,  which  are  generally  poisonous.  It  is,  however 
only  in  the  best  appointed  operating  rooms  of  hospitals  that 
this  most  modern  surgical  method  can  be  used,  because  the 
number  of  preventive  measures  against  bacteria,  which  must 
be  paid  attention  to,  is  enormous. 

Carbolic  acid  is  closely  related  to  benzene ;  like  that  com- 
pound, it  is  obtained  by  distilling  coal  tar.  Carbolic  acid 
contains  only  one  atom  of  oxygen  in  addition  to  the  con- 
stituents of  benzene,  and  has  the  following  constitution  : 

H  H 

i  i 

H  H-Cr^C-O-H 

H  H-ckx'c-H 

C  C 

i  i 

Benzene.  Carbolic  acid. 

The   great   advance   made   by   Lister   will   become    more 
evident   if  we   carry  our   thoughts  back  to  the  time  of  the 
20 


306  CHEMISTRY  IN   DAILY  LIFE 

Franco-German  war— that  is,  to  the  beginning  of  1870.  At 
that  time  the  universal  custom  was,  as  it  had  been  for 
centuries,  to  pick  lint  from  old  linen,  without  taking  due 
precautions,  and  also  without  any  suspicion  of  the  enormous 
number  of  infectious  substances  that  might  be  brought  into 
the  wounds  by  a  material  prepared  in  that  way  and  not 
subjected  to  disinfection.  It  is  certain  that  the  use  of  such 
lint  caused  the  death  of  many  who  would  have  been  saved 
to-day.  Lint  is  not  used  now,  for  it  has  been  replaced  by 
bandages  that  have  been  sterilised,  and  so  made  entirely  free 
from  bacteria.  As  everything  that  is  allowed  to  touch  a 
wound  nowadays,  including  the  hands  of  the  operator,  has 
been  disinfected  beforehand,  most  of  the  wounds  heal 
without  festering.  Severe  operations  are  of  course  still 
attended  with  danger,  but  what  used  to  be  the  commonest 
source  of  danger,  namely,  fever  following  the  wound,  is  as 
good  as  abolished.  And  there  are  many  operations  that  are 
practicable  since  the  discovery  of  the  antiseptic  treatment 
which  would  certainly  have  been  followed  in  former  times  by 
suppuration  leading  to  death. 

There  is  nowadays  an  enormous  number  of  antiseptics, 
and  carbolic  acid  has  very  many  competitors ;  at  the  same 
time  the  need  and  the  demand  for  antiseptics  keep  increasing 
because  of  the  great  advances  that  are  being  made  in 
bacteriology  and  hygiene. 

lodoform,  a  substance  already  mentioned,  has  kept  its 
position  in  the  treatment  of  wounds  in  quite  a  wonderful  way, 
notwithstanding  its  abominable  odour.  The  bacteriologists, 
however,  often  require  a  much  more  active  and  odourless 
substance,  and  for  this  purpose  they  generally  make  use  of 
corrosive  sublimate,  which,  chemically  considered,  is  chloride 
of  mercury.  An  aqueous  solution  of  this  compound  has  the 
most  powerful  antiseptic  action  even  when  it  is  greatly 


SALICYLIC  ACID  307 

diluted  ;  and  were  the  compound  not  so  extremely  poisonous 
it  would  probably  drive  out  almost  all  other  antiseptics. 

The  public  also  require  antiseptics  which  shall  be  quite 
odourless  and  tasteless,  and  not  in  the  least  poisonous,  for 
making  foods  keep  well,  for  instance.  Salicylic  acid  is  on  the 
whole  most  favoured  for  this  purpose.  This  acid  was  first 
obtained  in  1839  from  the  bark  of  the  willow  (salix),  and  the 
name  then  given  to  it  to  recall  its  origin  has  been  retained. 
The  investigation  of  the  arrangement  of  the  atoms  in  this 
compound  has  shown  that  it  is  very  closely  related  to 
carbolic  acid,  from  which  it  can  be  prepared  by  replacing  a 
certain  one  of  the  hydrogen  atoms  by  the  atomic  complex 
COOH  which  is  called  carboxyl* 

H  H 

i 

C—O-H 

H— CV^'C— H  H— C\^'C—  COOH 

C 

I 

H  H 

Carbolic  acid.  Salicylic  acid. 

*  It  should  be  remarked  that  chemical  formulas  have  been  used  in 
this  book  to  express  only  the  qualitative  composition  of  compounds. 
Formulae  mean  much  more  than  this  to  chemists.  They  tell  them  the 
weight-relations  between  the  elements  which  compose  the  compound 
formulated.  The  weights  of  the  atoms  of  the  individual  elements, 
relatively  to  one  another,  are  determinable  and  haye  been  determined. 
These  weights  are  referred  to  that  of  hydrogen,. the  lightest  of  the 
elements,  the  atomic  weight  of  which  is  taken  as  unity.  Tfce  atom  of 
carbon,  for  example,  is  twelve  times  heavier,  and  the  atom  of  oxygen  is 
sixteen  times  heavier,  than  the  atom  of  hydrogen.  This  knowledge 
makes  possible  the  universal  chemical  sign-language,  which  demands 
no  special  linguistic  knowledge,  but  is  equally  intelligible  to  th«  chemists 
of  all  nations.  As  Mack  very  rightly  observes,  the  chemical  sign- 
language,  in  its  great  simplicity  and  universal  intelligibility,  is  comparable 
only  with  the  notation  of  music. 

The  subject  of  chemical  notation  is  treated  more  fully  in  the  author's 
Introduction  to  Modern  Scientific  Chemistry  (H.  Grevel  &  Co.,  1901). 


308  CHEMISTRY   IN    DAILY    LIFE 

Salicylic  acid  is  now  manufactured  in  large  quantities  from 
carbolic  acid,  which  is  obtained  from  coal  tar,  by  a  method  that 
has  gradually  been  brought  to  the  greatest  perfection.  One 
kilo,  of  salicylic  acid  costs  about  2\  marks  [about  is.  ^d. 
per  lb.]. 

On  the  other  hand,  experience  has  shown  that  certain 
substances  obtained  from  tar,  which  have  very  great  antiseptic 
powers,  can  be  used  for  all  sorts  of  disinfecting  purposes  with- 
out being  more  than  superficially  purified,  provided  their 
other  properties  do  not  interfere  with  their  use  for  these 
purposes.  These  substances  can  therefore  be  obtained  at  an 
extremely  small  cost,  and  by  using  them  poorer  people  can 
themselves  prevent  many  illnesses,  and  stop  the  spread  of 
infection. 

And  thus  it  is  that  work  in  the  domain  of  chemistry 
advances  without  rest  in  ways  of  which  we  have  learnt 
something,  and  everything  that  nature  puts  before  us  is  tried 
in  all  directions  and  with  the  greatest  earnestness,  whether 
it  be  for  the  purpose  of  advancing  pure  science,  or  whether 
the  aim  be  the  good  of  mankind  or  that  of  the  individual 
man. 

Here  one  must  say — fermentation  is  classification.  This 
book  has  had  many  important  additions  made  to  it  since 
its  first  appearance  sixteen  years  ago. 

The  criticism  of  Francis  Bacon,  Lord  Verulam,  is  no  longer 
applicable  :  "  Chymicorum  autem  genus  ex paucis  experimentis 
fornacis  philosophiam  constituerunt  phantasticam  et  ad  pauca 
spectantem  "  ;  which  may  be  freely  rendered,  "  The  craft  of 
the  chemists,  from  a  few  experiments  made  in  the  furnace, 
has  constructed  a  philosophy  which  is  fantastical  and  has 
regard  to  but  a  few  phenomena."  No  longer,  as  in  the  olden 
days,  is  the  whole  covered  with  the  mantle  of  alchemistic 
mystery,  but  it  lies  open  before  us.  The  attempt  is,  there- 


CONCLUSION  309 

fore,  thoroughly  justified  to  give,  to  him  who  stands  outside, 
a  glimpse  into  this  world  of  keen  intellectual  activity,  which 
should  increase  his  general  intelligence  and  quicken  the 
special  direction  of  his  thought.  As  this  book  has  been 
translated  into  all  the  chief  languages,  the  author  believes 
that  the  method  he  has  adopted  for  diffusing  general  chemical 
knowledge  will  be  found  not  unsuitable  for  his  purpose. 


INDEX 


Abraum  salz,  46 

Acetic  acid,  1 16,  119 

Acetone,  119,  129 

Acetylene,  35 

Acid  carbonate  of  ammonia,  187 

Acid  carbonate  of  soda,  187 

Acid  sulphite  of  lime,  172 

Acids,  49 

Air,  composition  of,  8  ;  constituents 

of,    7,    27,   47  ;    pressure    of,    5, 

75  ;  weight  of,  3 
Albumen,   coagulation   of,    56  ;    in 

various    foods,  89  ;     use    of,    in 

photography,  226 
Albuminoids,  56,  57,  61,  90 
Alchemy,  245 
Alcohol,  85,  103  ;    as  a  food,  115  ; 

quantity  in  beer,  102  ;    in  wine, 

95  ;  in  spirits,  107,  114 
Alcohol,  absolute,  in 
Alizarin,  156 
Alkali,  49,  177 

Alkaline     pyrogallate     in     photo- 
graphy, 228 
Alkaloids,  294 
Alloys,  287 
Alum,  140,  149  ;  use  of,  in  dyeing, 

149  ;  in  tanning,  140 
Alumina,  141,  142,  283 
Aluminium,  282,  285 
Amalgams,  204 
Amber,  1 59 
Ammonia,  29,49 
Ammonia  soda  process,  187 


Ammonia  water,  29 
Amptre,  23  note 
Amylic  alcohol,  109 
Anaesthetics,  302 
Aniline  black,  162 
Aniline  colours,  153,  298 
Animal  charcoal,  42 
Anode,  235 
Anthracene,  153 
Antichlor,  146,  167 
Antipyrin,  301 
Antiseptics,  304 
Aqua  fortis,  181 
Argon,  8 

Aroma  of  wines,  95 
Arrac,  114 
Arrowroot,  67 
Artificial  butter,  65 
Artificial  fodder,  60 
Artificial  gems,  207 
Artificial  horsehair,  135 
Artificial  leather,  131 
Artificial  silk,  1 34 
Artificial  wool,  133 
Ash  analysis,  37 
Atom,  24 

Atomic  weights,  307  note 
Atropine,  295 

BACON  and  peas,  92 
Baking,  84 
Baking  powder,  87 
Barilla,  178,  185 
Barley,  too 


3I2 


INDEX 


Barometer,  5 

Base  metals,  241,  252 

Bases,  49 

Beefsteak,  81 

Beer,  99,  102 

Beetroot  sugar,  73 

Benzene,  298 

Bessemer  steel,  271 

Beverages,  77,  93 

Bicarbonate  of  ammonia,  187  ;    of 

soda,  187 

Bichromate  of  potash,  232 
Bimetallism,  243 
Biscuit  porcelain,  219 
Blast  furnace,  258,  260  note,  263 
Blasting  gelatin,  129 
Bleaching,  144,  167 
Bleaching  powder,  145,  167 
Blendes,  241  note 
Blueing  washed  linen,  144 
Body,    maintenance    of    tempera- 
ture of,  ii,  91 
Boilers,  108,  173,  267 
Boiling   under   increased   pressure, 
108  ;   under  reduced  pressure,  75 
Bonbon  making,  71 
Bones,  41  ;  fat  of,  41,  193 
Boric  acid,  202 
Bran,  68 
Brandy,  114 
Brass,  289 
Brazilwood,  157 

Bread,  86 

Bread,  black,  92 

Breath,  expired,  10 

Breathing,  i,  n 

Bricks,  209 

Britannia  metal,  291 

Bromide  of  ammonium,  229 

Bromide  of  silver,  222,  229 

Bromine,  46 

Bronze,  288 

Bunsen's  burners,  33 

Butter,  65  ;  artificial,  65 

CALAMINE, 290 
Calcined  soda,  186 


Calcining,  42,  186,  188 

Calcium  carbide,  35,51 

Calcium  nitride,  51 

Calcium  oxide,  177 

Calico  printing,  158 

Camera  obscura,  224 

Camphor,  103  note 

Candle  light,  17,  1 8 

Candles,  snuffing  of,  19 

Cane  sugar,  72 

Carbohydrates,  56,  64 

Carbolic  acid,  128,  153,  305 

Carbon,  n,  16,  21,  91,  252 

Carbon,  bisulphide  of,  30 

Carbon  monoxide,  252,  260  note 

Carbonic  acid,  12,  32,  85,  126,  187 

Carbonic  acid  in  beer,  102 

Carbonic  acid  in  expired  breath,  10 

"Carbonising,"    134 

Casein,  57 

Cast  glass,  204 

Cast  iron,  253,  258,  260,  261 

Cast  steel,  270 

Catechu,  139 

Caustic  lime,  177,  207 

Caustic  potash,  177,  191 

Caustic  soda,  191 

Cellite,  131 

Celluloid,  131 

Cellulose,  69,  125,  169,  171 

Cementation  steel,  269 

Cements,  211 

Cerotic  acid,  20 

Chalk,  176,  1 88,  191,  202 

Chamois  leather,  141 

Champagne,  96 

Charcoal,  16,  107 

Chemical  formulae,  23,  130,  307  note 

Chemistry,  differences  between,  and 

physics,  i,  2 
Chili  saltpetre,  49,  50 
Chloral,  301 

Chlorate  explosives,  130 
Chlorate  of  potash,  130 
Chloride  of  ammonium,  189 
Chloride  of  calcium,  146,  189 
Chloride  of  lime,  145,  184 


INDEX 


313 


of 


Chloride  of  silver,  222 
Chlorine,  145,  184,  189 
Chloroform,  301,  303 
Chlorophyll-grains,  36,  67 
Chromegelatin,  232 
Chrome  leather,  142 
Chrome  yellow,  160 
Chromium  oxide,  142,  150,  220 
Cider,  96 

Circulation  of  the  blood,  n 
Clay,  209  ;   modelling  in,  212 
Coagulation   of   albumen,    56 

blood,  59  ;  of  milk,  57 
Coal  gas,  28 
Coal   tar,  29,   153;    colours,   153, 

157 
Cobalt,  1 60  ;  chloride  of,  163  ;  oxide 

of,  220 
Cocaine,  295 
Cochineal,  151 

Cocoanut  butter,  195  ;  oil,  195 
Coffee,  77,  138 
Coinage,  287 
Coke,  29,  262 

Collodion,  128  ;    use  of,  in  photo- 
graphy, 227 
Colophony  resin,  196 
Colour  photography,  234 
Combustion,  7,  n 
Common  salt,  179, 187,  194,  214 
Condiments,  77 
Congo  red,  152 
Coniine,  299 
Cooking,  77,  78 
Cooking  by  gas,  33 
Copal,  162 

Copper,  281,  289  ;   chloride  of,  163 
Copying  ink,  163 
Cordite,  130 

Corrosive  sublimate,  306 
Cotton,  144 

Cotton,  dyeing  of,  148,  1 50,  i  52 
Cotton-seed  oil,  65,  161 
Cream,  57,  91 

Crops,  productiveness  of ,  52  ;  rota- 
tion of ,  38 
Crucible  steel,  271 


Cryolite,  209 

Crystallisation,  water  of,  186 
Cuivre  poli,  290 

DAGUERREOTYPES,  225 

"  Degras,"  143 

Denaturalised  spirit,  112 

Dephosphorising  iron,  273 

Developers,  225,  227 

Dextrin,  71 

Diabetic  patients,  diet  of,  70  note, 

76,  90,  95 
Diastase,  100,  105 
Diazo  compounds,  152 
Diffusion,  9 
Digestion,  53,  60 
Dioxyanthraquinone,  1 56 
Diphtheria  serum,  59 
Disinfection,  305 
Distillation,  25,  102  note,  no 
Distillation,  dry,  28 
Dough,  84 

Drinks,  spirituous,  85,  93 
Dry  plates  (photographic),  229 
Ducat,  origin  of  word,  247 
Dyeing,  147 
Dyeing  extracts,  1 57 
Dynamite,  127 

EARTH,  infusorial,  127 

Eau  de  Javelle,  146 

Effervescing  wines,  96 

Eggs,  91  note 

Electric  furnace,  25,  292 

Electric  lamps,  293 

Electro-deposition  of  metals,  284 

Electrolysis,  285 

Elements,  2 1 

Emanation  of  radium,  239 

Eosin,  163 

Esparto  grass,  169 

Ethane,  23,  297 

Ether,  302 

Evaporation   under   reduced    pre 

sure,  75 
Excise  duties  on  spirits,  112 


INDEX 


FALLOW,  39 

Fats,  19,  64,  192 

Fatty  acids,  20,  192 

Fayence,  215 

Felspar,  217 

Felting  cloth,  132 

Felting  paper  pulp,  165,  168 

Fermentation,  85,  93,  96,  101 

Fermented  liquors,  93 

Ferrous  sulphate,  227 

Fibres,  animal  and  vegetable,  132 

Fibrin,  53 

Fir  wood,  173 

Fire-clay,  212 

Fireworks,  131 

Fitted  soap,  195 

Flame,  nature  of,  17,  33 

Florin,  origin  of  word,  247 

Flowers,  manuring  of,  41  note 

Fluorescence,  236 

Fodder,  60 

Foods,  56,  63,  76,  89 

Forging  iron,  253 

Fruit  ethers,  95,  113 

Fruits,  fermentation  of,  94] 

Fruits,  ripening  of,  69 

Fuchsin,  148,  163 

Fulling  cloth,  132 

Fulminating  mercury,  125 

Furriery,  141 

Fusel  oil,  109 

GALENA,  213 

Gallotannate  of  iron,  162 

Galls,  162 

Gambier,  139 

Garden  manure,  41  note 

Gas,  28 

Gas,  cooking  by,  33 

Gas  generators,  277 

Gas-lights,  incandescent,  34 

Geissler  tubes,  235 

Gelatin,  61 

Gelatin  emulsion  process,  229 

Gems,  artificial,  207 

Glances,  241  note 

Glass,  199,  200,  203,  207 


Glass,  colouring  of,  207 

Glauber's  salt,  180,  186 

Glazes,  213 

Glove  leather,  141 

Glucose,  71,  85,  94 

Glue,  61 

Gluten,  84 

Glycerin,  19,  161,  192 

Gold,  220,  242  ;  production  of ,  245 

Gold  purple,  207 

Gold  standard,  243,  245 

Grape  sugar,  66,  7 1 

Greek  fire,  121 

Guano,  42 

Guncotton,  125 

Gunpowder,  123 

Gypsum,  44,  170 

HARD  soap,  193,  194 
Hartshorn,  salts  of,  87 
Hartshorn,  spirits  of,  30 
Helium,  8 
Hides,  136 

High-fermentation  beer,  101 
Hoffman's  drops,  302  note 
Honey,  98 
Hops,  100 

Hydraulic  cements,  211 
Hydrocarbons,  21,  296 
Hydrochloric  acid,  183,  184 
Hydrochloric  acid  in  the  stomach, 

53,6o 

Hydrogen,  22 
Hydrogen  peroxide,  147 
Hydroquinone,  227 
Hyposulphite  of  soda,  146,  226 

latro  chemists,  294 
Incandescent  gas-lights,  34 
Indelible  ink,  221 
Indigo,  154 
Indulin  black,  162 
Ink,  162 

Inorganic  salts,  49 
Iodide  of  silver,  222 
Iodine,  51 
lodoform,  304 


INDEX 


315 


Iron,  53,  256  ;  output  of,  in  different 

countries,  255  note 
Iron  in  foods,  80 

KAIRINE,  301 
Kaolin,  217 
Kathode  rays,  235 
Kid-glove  leather,  141 
Koumiss,  98 
Krypton,  8 

LACTIC  acid,  57,  85 

Lactic  fermentation,  57,  87,  98,  137 

Lakes,  150 

Lead  glance,  241  note 

Lead  glass,  206 

Lead  glaze,  213,  214 

Lead  oxide,  161,  206 

Lead  soap,  198 

Leaden  chambers,  180 

Leaden  pipes  173 

Leather,  136,  140,  141,  143 

Leblanc  soda  process,  179 

Lighting-gas,  33 

Lime,  176,  177,  188,  197,  210 

Lime-sandstone  bricks,  211 

Limestone,  176,  210 

Linen,  144 

Linoleic  acid,  160 

Linoleum,  162 

Linseed  oil,  160 

Liqueurs,  113 

Loading  paper,  170 

Loading  soap,  194 

Logwood,  157 

Low-fermentation  beer,  101 

Lunar  caustic,  221 

MADDER,  155 

Majolica,  216 

Malt,  100 

Manganese,  272  ;  peroxide  of,  184 

Manures,  37  ;    artificial,  44,  46,  48, 

50.  5i,  52 
Margarine,  65 
Marsh-gas,  23 
Mashing  process,  100 


Matches,  13 

Mead,  98 

Meal.  68 

Melinite,  128 

Mercerised  cotton-wool,  134 

Mercury,  204 ;    poisoning   by,    205 

Metals,  241,  252 

Methane,  23 

Methylated  spirit,  112 

Milk,  curdling  of,  57  ;  fermentation 

of,  98  ;  nourishing  value  of,  91 
Milk  glass,  208 
Milk-sugar,  57,  94  note 
Milling  cloth,  132 
Mirrors,  204 
Mixed  diet,  64,  90 
Molasses,  76,  190 
Molecule,  24 
Mordants,  149,  151 
Morphine,  295,  301 
Mortars,  210 
Mother-liquor,  51 
Muffle  furnace,  220 
"  Mungo."  134 
Must,  94 
Mustard,  77 
Mycodertna  aceti,  1 1 7 
Myricyl  alcohol,  20 

NAPHTHALENE, 153 

Narcotics,  295 

Negatives  (photographic),  224,  227 

Neon,  8 

Nickel  coins,  288 

Nickel  silver,  290 

Nickel,  steel,  291 

Nitragin,  49 

Nitrate  of  potash,   130;    of  silver, 

221  ;  of  soda,  50 
Nitre,  50,  120 
Nitric  acid,  51,  i8r 
Nitroacid,  125,  128 
Nitrocellulose,  120,  127 
Nitrogen,  7,  47  ;  assimilation  of,  by 

plants,  47  ;  gatherers  of,  48 
Nitroglycerin,  127 
Nitrogroups,  125,  128 


INDEX 


Noble  metals,  241 

Nourishment,    absorption    of,    53  ; 

means    of,    89 ;     quantities    of, 

necessary,  90 

OAK  bark,  138 

Oilcake,  60,  196 

Oil  colours,  1 60 

Oil,  lighting  by,  21 

Oil  painting,  1 59 

Oil  tanning,  142 

Oils  becoming  rancid,  161 

Oils,  drying,  160 

Oleic  acid,  19,  160 

Oleomargarine,  65 

Olive  oil,  21,  1 60 

Open  flame  furnaces,  280 

Opium,  295 

Ores,  241,  252 

Orthochromatic     photographic 

plates,  232 
Osram  lamps,  293 
Oxidation,  7 
Oxides,  7,  252 
Oxygen,     7,     n  ;      absorption    of, 

by  the  blood,  9 
Ozone,  27 

PAINTING,  160 

Palm  oil,  196 

Palmitic  acid,  19 

Paper,  164,  165,  169 

Papyrus,  164 

Paraffin,  20,  27  ;   candles,  20,  27 

Parchment,  143,  164 

Parting  acid,  181 

Patents,  172 

Patina,  289 

Peat,  278 

Pepper,  77 

Pepsin,  53,  60 

Peptones,  53,  60 

Persil,  147 

Perry,  96 

Petroleum,  21,  25 

Petroleum  ether,  26 

Phenacetin,  301 


Phosphates  made  soluble,  43,  44 

Phosphoric  acid,  41,  43,  275 

Phosphorite,  42 

Phosphorus,  13,  273  ;  red,  14,  15 

Photography,  221 

Photography  in  colours,  234 

Physics  and  chemistry,  relations 
between,  i,  2 

Picric  acid,  128 

Pig  iron,  253, 255,  258,  260,  261,  273 

Pig  suet,  19 

Pigment  printing,  232 

Plant  albumen,  59 

Plant  ashes,  37 

Plants,  food  of,  36,  41  note 

Plasters,  198 

Plate  glass,  204 

Platinocyanide  of  barium,  236 

Platinum,  242 

Porcelain,  209, 216  ;  painting  of,  220 

Potash,  caustic,  177,  191 

Potash  salts,  178,  190 

Potashes,  45,  178 

Potassium,  284 

Potassium  cyanide,  243 

Potato  spirit,  107,  109 

Potatoes,  68  ;  boiling  of ,  88  ;  grow- 
ing of,  for  making  sprits,  107 

Potter's  wheel,  213 

Pottery,  209,  213 

Powder,  smokeless,  125,  130 

Pressed  yeast,  105 

Prismatic  powder,  1 24 

Propane,  23 

Proteids,  60 

Prussian  blue,  149 

Puddling,  265 

Pyridine,  299  ;  bases,  113  note 

Pyrites,  182,  241  note 

Pyrogallic  acid,  227 

Pyrolusite,  184 

QUARTZ,  206 
Quartz  glass,  206 
Quebracho  wood,  139 
Quinine,  295,  299 
Quinoline,  300 


INDEX 


RADIO-ACTIVE  substances,  239 
Radium,  239 
Rags,  165 
Rails,  267,  268 
Railways,  268 
Rape  oil,  21 
Rare  metals,  293 
Red  rays,  231 
Regenerative  furnaces,  280 
Regenerators,  279 
Rennet,  58 
Resins,  161,  196 
Retouching  (photographs),  231 
Reverberatory  furnace,  265 
Roasting  ores,  252 
Rolling  iron,  266 
Rontgen  rays,  234,  236 
Roots,  73,  156 
Rotation  of  crops,  38 
Rubies,  208 
Ruby  glass,  207 
Rum,  114 
Rusting  of  iron,  7 

Rye,  68,  91  ;  growing  of,  for  making 
spirits,  107 

SACCHARIN,  76 

Saccharomyces  cerevisia,  94 

Sack,  96  note 

Safety-matches,  14 

Sago,  67 

Salammoniac,  188 

Salicylic  acid,  307 

Salt,  common,  179,  183,  193,  214 

Salting  soaps,  194 

Saltpetre,  50,  120,  122,  181 

Salts,  49 

Sand, 200, 210,  212 

Sapphires,  208 

Sequin,  origin  of  word,  247 

Serum,  59 

Shellac,  162 

"  Shoddy,"  134 

Silica,  199 

Silicates,  200,  211 

Silicic  acid,  200 

Silicon,  272  note 


Silk,  132,  134 

Silvalin,  174 

Silver,  243 

Silvering  glass,  205 

Sintering,  210 

Size,  166 

Sizing  paper,  166 

Slag,  212,  258 

Slaked  lime,  177,  207 

Smalt,  1 60 

Smokeless  powder,  125,  130 

Soap,  hard,  193,  194  ;   loaded,  194  ; 

soft,  193 

Soaps,  191,  192,  194 
Soda,  176,  179,  187  ;  calcined,  186; 

caustic,  191 
Soda  cellulose,  171 
Soda  crystals,  1 80 
Sodium,  285 

Soft  iron,  280  ;  steel,  277,  280 
Soup,  nourishing  value  of,  83 
Soxhlet's  apparatus,  58 
Spiegeleisen,  272 
Spirits,  104,  in 
Starch,  67,  88,  100,  105 
Starch-sugar,  69 
Stassfurt  salt  deposits,  46 
Stearic  acid,  19 
Stearin  candles,  20 
Steel,  253,  269,  271,  277,  292 
Sticking  plaster,  198 
Stoneware,  214 
Strass,  207 
Straw,  170 

Sublimate,  corrosive,  306 
Substantive  colours,  152 
Suet,  19 

Sugar,  69,  72,  73,  85,  95 
Sugar  refining,  74 
Sulphate  of  ammonia,  50  ;   of  soda, 

179,202 

Sulphide  of  soda,  137 
Sulphite  cellulose,  171,  173 
Sulphite  of  lime,  171 
Sulphobenzimide,  76 
Sulphur,  172,  1 80  ;  in  coal  gas,  30 
Sulphur- matches,  13 


INDEX 


Sulphuric  acid,   31,    180,    181,   202 

note 

Sulphurous  acid,  147,  172,  180,  246 
Sumac,  139 
Superphosphates,  44 
Sweating  skins,  137 
Sympathetic  inks,  163 
Syntheses,  296 

TALBOTYPES,  223 

Tallow,  65 

Tallow  candles,  19 

Talmi  gold,  290 

Tannin,  138,  151 

Tanning  extracts,  139 

Tanning  stuffs,  138 

Tantalum  lamps,  293 

Tar,  28,  153  ;  tar  colours,  153 

Taxing  spirits,  112  ;   sugar,  73 

Tea,  138 

Tetrazo  bodies,  153 

Thomas's  phosphate  meal,  45 

Tin,  150  ;    chloride  of,  150  ;    oxide 

of,  216 

Tin  composition,  150 
Tinfoil,  204 
Tombac,  290 
Torpedoes,  126 
Trypsin,  54 
Tungsten  lamps,  293 
Turbines,  292 
Turkey  red,  152 
Turpentine  oil,  103  note 
Tuyeres,  260  note 
Type  metal,  291 

ULTRA-VIOLET  rays,  231 
Uranium  compounds,  239 
Uranium  oxide,  220 
Urea,  56 

VARNISHES,  161 
Vaseline,  27 
Veal  cutlets,  8 1 


Vegetarianism,  89 

Vinasse,  109 

Vinegar,  117;   essence,  1 1 8 

Violet  rays,  231 

Volt,  23  note 

WARP,   132 

Wash  leather,  143 

Water,    66  ;     electrolysis   of,    284 
hard  and  soft,  198  ;  of  crystallisa- 
tion, 1 86 

WTater  glass,  199 

Wax  candles,  20 

Welding  iron,  254 

Wheat,  average  yield  of,  52 

Wheaten    bread,    84  ;     meal,    68  ; 
starch,  67 

White  light,  231 

White  of  egg,  digestibility  of ,  53,  60- 

White  tanning,  141 

Window  glass,  204 

Wine  vinegar,  117 

Wines,  94 

Woad,  154 

Wood,  1 6,  169 

Wood  charcoal,  16 

Wood,  dry  distillation  of,  28,  119 

Wood  gas,  119 

Wood  spirit,  1 19 

Wood  vinegar,  1 1 9 

Woof,  132 

Wool,  132,  148 

Wool  washings,  ashes  of,  196 

Wort,  100 

Wrought  iron,  253,  261,   264,    265,. 
266 

XENON,  8 

YEAST,  85,  86,  93,  105 
Yolk  of  eggs,  141 

ZINC,  282 

Zinc  blende,  241  note 


Printed  by  Maxell,  Watson  &•  Viney,  Ld.,  London  and  A ylcsbury,  England. 


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